lspci -vvv gives:

04:09.0 Ethernet controller: Atheros Communications Inc. AR2413 802.11bg NIC (rev 01)
	Subsystem: Device 17f9:0018
	Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Latency: 168 (2500ns min, 7000ns max), Cache Line Size: 32 bytes
	Interrupt: pin A routed to IRQ 17
	Region 0: Memory at fdce0000 (32-bit, non-prefetchable) [size=64K]
	Capabilities: <access denied>
	Kernel driver in use: ath5k
	Kernel modules: ath5k

Here's a snip from /var/log/syslog while encountering the problem:   

Aug  3 12:47:16 stlinux wpa_supplicant[1617]: Trying to associate with 00:3a:98:32:e5:33 (SSID='xxxxxxxxxxxxxxx' freq=2437 MHz)
Aug  3 12:47:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  completed -> associating
Aug  3 12:47:16 stlinux kernel: [  169.108031] wlan0: deauthenticating from 00:3a:98:32:8b:33 by local choice (reason=3)
Aug  3 12:47:16 stlinux kernel: [  169.199787] wlan0: direct probe to AP 00:3a:98:32:8b:33 (try 1)
Aug  3 12:47:16 stlinux kernel: [  169.199803] wlan0: deauthenticating from 00:3a:98:32:8b:33 by local choice (reason=3)
Aug  3 12:47:16 stlinux wpa_supplicant[1617]: Association request to the driver failed
Aug  3 12:47:16 stlinux wpa_supplicant[1617]: CTRL-EVENT-DISCONNECTED - Disconnect event - remove keys
Aug  3 12:47:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associating -> disconnected
Aug  3 12:47:16 stlinux kernel: [  169.241965] wlan0: direct probe to AP 00:3a:98:32:e5:33 (try 1)
Aug  3 12:47:16 stlinux kernel: [  169.261987] wlan0: direct probe responded
Aug  3 12:47:16 stlinux kernel: [  169.261993] wlan0: authenticate with AP 00:3a:98:32:e5:33 (try 1)
Aug  3 12:47:16 stlinux kernel: [  169.338994] wlan0: authenticated
Aug  3 12:47:16 stlinux kernel: [  169.339020] wlan0: associate with AP 00:3a:98:32:e5:33 (try 1)
Aug  3 12:47:16 stlinux wpa_supplicant[1617]: Associated with 00:3a:98:32:e5:33
Aug  3 12:47:16 stlinux wpa_supplicant[1617]: CTRL-EVENT-CONNECTED - Connection to 00:3a:98:32:e5:33 completed (reauth) [id=0 id_str=]
Aug  3 12:47:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  disconnected -> associated
Aug  3 12:47:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associated -> completed
Aug  3 12:47:16 stlinux kernel: [  169.342027] wlan0: RX AssocResp from 00:3a:98:32:e5:33 (capab=0x401 status=0 aid=2)
Aug  3 12:47:16 stlinux kernel: [  169.342031] wlan0: associated
Aug  3 12:47:17 stlinux NetworkManager: <debug> [1280857637.001031] periodic_update(): Roamed from BSSID 00:3A:98:32:8B:33 (xxxxxxxxxxxxxxx) to 00:3A:98:32:E5:33 (xxxxxxxxxxxxxxx)
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: Trying to associate with 00:3a:98:32:8b:33 (SSID='xxxxxxxxxxxxxxx' freq=2462 MHz)
Aug  3 12:48:36 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  completed -> associating
Aug  3 12:48:36 stlinux kernel: [  249.236032] wlan0: deauthenticating from 00:3a:98:32:e5:33 by local choice (reason=3)
Aug  3 12:48:36 stlinux kernel: [  249.306024] wlan0: direct probe to AP 00:3a:98:32:e5:33 (try 1)
Aug  3 12:48:36 stlinux kernel: [  249.317486] wlan0: direct probe responded
Aug  3 12:48:36 stlinux kernel: [  249.317492] wlan0: authenticate with AP 00:3a:98:32:e5:33 (try 1)
Aug  3 12:48:36 stlinux kernel: [  249.320332] wlan0: deauthenticating from 00:3a:98:32:e5:33 by local choice (reason=3)
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: Association request to the driver failed
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: CTRL-EVENT-DISCONNECTED - Disconnect event - remove keys
Aug  3 12:48:36 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associating -> disconnected
Aug  3 12:48:36 stlinux kernel: [  249.353235] wlan0: direct probe to AP 00:3a:98:32:8b:33 (try 1)
Aug  3 12:48:36 stlinux kernel: [  249.355769] wlan0: direct probe responded
Aug  3 12:48:36 stlinux kernel: [  249.355775] wlan0: authenticate with AP 00:3a:98:32:8b:33 (try 1)
Aug  3 12:48:36 stlinux kernel: [  249.358626] wlan0: authenticated
Aug  3 12:48:36 stlinux kernel: [  249.358646] wlan0: associate with AP 00:3a:98:32:8b:33 (try 1)
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: Associated with 00:3a:98:32:8b:33
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: CTRL-EVENT-CONNECTED - Connection to 00:3a:98:32:8b:33 completed (reauth) [id=0 id_str=]
Aug  3 12:48:36 stlinux kernel: [  249.362857] wlan0: RX AssocResp from 00:3a:98:32:8b:33 (capab=0x401 status=0 aid=1)
Aug  3 12:48:36 stlinux kernel: [  249.362861] wlan0: associated
Aug  3 12:48:36 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  disconnected -> associated
Aug  3 12:48:36 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associated -> completed

*************

Here's a snip from /var/log/daemon.log:

Aug  3 12:45:01 stlinux NetworkManager: <info>  Activation (wlan0) starting connection 'Auto xxxxxxxxxxxxxxx
Aug  3 12:45:01 stlinux NetworkManager: <info>  (wlan0): device state change: 3 -> 4 (reason 0)
Aug  3 12:45:01 stlinux NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) scheduled...
Aug  3 12:45:01 stlinux NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) started...
Aug  3 12:45:01 stlinux NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) scheduled...
Aug  3 12:45:01 stlinux NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) complete.
Aug  3 12:45:01 stlinux NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) starting...
Aug  3 12:45:01 stlinux NetworkManager: <info>  (wlan0): device state change: 4 -> 5 (reason 0)
Aug  3 12:45:01 stlinux NetworkManager: <info>  Activation (wlan0/wireless): connection 'Auto xxxxxxxxxxxxxxx' requires no security.  No secrets needed.
Aug  3 12:45:01 stlinux NetworkManager: <info>  Config: added 'ssid' value 'xxxxxxxxxxxxxxx'
Aug  3 12:45:01 stlinux NetworkManager: <info>  Config: added 'scan_ssid' value '1'
Aug  3 12:45:01 stlinux NetworkManager: <info>  Config: added 'key_mgmt' value 'NONE'
Aug  3 12:45:01 stlinux NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) complete.
Aug  3 12:45:01 stlinux NetworkManager: <info>  Config: set interface ap_scan to 1
Aug  3 12:45:01 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  scanning -> disconnected
Aug  3 12:45:01 stlinux wpa_supplicant[1617]: Failed to initiate AP scan.
Aug  3 12:45:01 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  disconnected -> scanning
Aug  3 12:45:02 stlinux wpa_supplicant[1617]: Trying to associate with 00:3a:98:32:8b:33 (SSID='xxxxxxxxxxxxxxx' freq=2462 MHz)
Aug  3 12:45:02 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  scanning -> associating
Aug  3 12:45:02 stlinux wpa_supplicant[1617]: Association request to the driver failed
Aug  3 12:45:02 stlinux wpa_supplicant[1617]: Associated with 00:3a:98:32:8b:33
Aug  3 12:45:02 stlinux wpa_supplicant[1617]: CTRL-EVENT-CONNECTED - Connection to 00:3a:98:32:8b:33 completed (auth) [id=0 id_str=]
Aug  3 12:45:02 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associating -> associated
Aug  3 12:45:02 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associated -> completed
Aug  3 12:45:02 stlinux NetworkManager: <info>  Activation (wlan0/wireless) Stage 2 of 5 (Device Configure) successful.  Connected to wireless network 'xxxxxxxxxxxxxxx'.
Aug  3 12:45:02 stlinux NetworkManager: <info>  Activation (wlan0) Stage 3 of 5 (IP Configure Start) scheduled.
Aug  3 12:45:02 stlinux NetworkManager: <info>  Activation (wlan0) Stage 3 of 5 (IP Configure Start) started...
Aug  3 12:45:02 stlinux NetworkManager: <info>  (wlan0): device state change: 5 -> 7 (reason 0)
Aug  3 12:45:02 stlinux NetworkManager: <info>  Activation (wlan0) Beginning DHCP transaction (timeout in 45 seconds)
Aug  3 12:45:02 stlinux NetworkManager: <info>  dhclient started with pid 2075
Aug  3 12:45:02 stlinux NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP6 Configure Get) scheduled...
Aug  3 12:45:02 stlinux NetworkManager: <info>  Activation (wlan0) Stage 3 of 5 (IP Configure Start) complete.
Aug  3 12:45:02 stlinux NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP6 Configure Get) started...
Aug  3 12:45:02 stlinux NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP6 Configure Get) complete.
Aug  3 12:45:02 stlinux dhclient: Internet Systems Consortium DHCP Client V3.1.3
Aug  3 12:45:02 stlinux dhclient: Copyright 2004-2009 Internet Systems Consortium.
Aug  3 12:45:02 stlinux dhclient: All rights reserved.
Aug  3 12:45:02 stlinux dhclient: For info, please visit https://www.isc.org/software/dhcp/
Aug  3 12:45:02 stlinux dhclient: 
Aug  3 12:45:02 stlinux NetworkManager: <info>  DHCP: device wlan0 state changed (null) -> preinit
Aug  3 12:45:02 stlinux dhclient: Listening on LPF/wlan0/00:1a:73:4e:37:a3
Aug  3 12:45:02 stlinux dhclient: Sending on   LPF/wlan0/00:1a:73:4e:37:a3
Aug  3 12:45:02 stlinux dhclient: Sending on   Socket/fallback
Aug  3 12:45:02 stlinux dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 5
Aug  3 12:45:04 stlinux avahi-daemon[1546]: Registering new address record for xxxxxxxxxxxxxxxxxxxxxxxx on wlan0.*.
Aug  3 12:45:07 stlinux dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 11
Aug  3 12:45:07 stlinux dhclient: DHCPOFFER of xxx.xxx.xxx.xxx from 3.3.3.3
Aug  3 12:45:07 stlinux dhclient: DHCPREQUEST of xxx.xxx.xxx.xxx on wlan0 to 255.255.255.255 port 67
Aug  3 12:45:07 stlinux dhclient: DHCPACK of xxx.xxx.xxx.xxx from 3.3.3.3
Aug  3 12:45:07 stlinux dhclient: bound to xxx.xxx.xxx.xxx -- renewal in 2968 seconds.
Aug  3 12:45:07 stlinux NetworkManager: <info>  DHCP: device wlan0 state changed preinit -> bound
Aug  3 12:45:07 stlinux NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP4 Configure Get) scheduled...
Aug  3 12:45:07 stlinux NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP4 Configure Get) started...
Aug  3 12:45:07 stlinux NetworkManager: <info>    address xxx.xxx.xxx.xxx
Aug  3 12:45:07 stlinux NetworkManager: <info>    prefix 21 (255.255.248.0)
Aug  3 12:45:07 stlinux NetworkManager: <info>    gateway xxx.xxx.xxx.xxx
Aug  3 12:45:07 stlinux NetworkManager: <info>    nameserver 'xxx.xxx.xxx.xxx'
Aug  3 12:45:07 stlinux NetworkManager: <info>    domain name 'xxxxxxxxx.xxx'
Aug  3 12:45:07 stlinux NetworkManager: <info>  Activation (wlan0) Stage 5 of 5 (IP Configure Commit) scheduled...
Aug  3 12:45:07 stlinux NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP4 Configure Get) complete.
Aug  3 12:45:07 stlinux NetworkManager: <info>  Activation (wlan0) Stage 5 of 5 (IP Configure Commit) started...
Aug  3 12:45:07 stlinux avahi-daemon[1546]: Joining mDNS multicast group on interface wlan0.IPv4 with address xxx.xxx.xxx.xxx.
Aug  3 12:45:07 stlinux avahi-daemon[1546]: New relevant interface wlan0.IPv4 for mDNS.
Aug  3 12:45:07 stlinux avahi-daemon[1546]: Registering new address record for xxx.xxx.xxx.xxx on wlan0.IPv4.
Aug  3 12:45:08 stlinux NetworkManager: <info>  (wlan0): device state change: 7 -> 8 (reason 0)
Aug  3 12:45:08 stlinux NetworkManager: <debug> [1280857508.228258] periodic_update(): Roamed from BSSID 00:0B:85:8B:8D:2C (xxxxxxxxxxxxxxx) to 00:3A:98:32:8B:33 (xxxxxxxxxxxxxxx)
Aug  3 12:45:08 stlinux NetworkManager: <info>  Policy set 'Auto xxxxxxxxxxxxxxx' (wlan0) as default for routing and DNS.
Aug  3 12:45:08 stlinux NetworkManager: <info>  Activation (wlan0) successful, device activated.
Aug  3 12:45:08 stlinux NetworkManager: <info>  Activation (wlan0) Stage 5 of 5 (IP Configure Commit) complete.
Aug  3 12:45:13 stlinux ntpdate[2203]: no server suitable for synchronization found
Aug  3 12:46:02 stlinux hp[2531]: io/hpmud/pp.c 627: unable to read device-id ret=-1
Aug  3 12:46:03 stlinux AptDaemon: INFO: Initializing daemon
Aug  3 12:47:16 stlinux wpa_supplicant[1617]: Trying to associate with 00:3a:98:32:e5:33 (SSID='xxxxxxxxxxxxxxx' freq=2437 MHz)
Aug  3 12:47:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  completed -> associating
Aug  3 12:47:16 stlinux wpa_supplicant[1617]: Association request to the driver failed
Aug  3 12:47:16 stlinux wpa_supplicant[1617]: CTRL-EVENT-DISCONNECTED - Disconnect event - remove keys
Aug  3 12:47:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associating -> disconnected
Aug  3 12:47:16 stlinux wpa_supplicant[1617]: Associated with 00:3a:98:32:e5:33
Aug  3 12:47:16 stlinux wpa_supplicant[1617]: CTRL-EVENT-CONNECTED - Connection to 00:3a:98:32:e5:33 completed (reauth) [id=0 id_str=]
Aug  3 12:47:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  disconnected -> associated
Aug  3 12:47:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associated -> completed
Aug  3 12:47:17 stlinux NetworkManager: <debug> [1280857637.001031] periodic_update(): Roamed from BSSID 00:3A:98:32:8B:33 (xxxxxxxxxxxxxxx) to 00:3A:98:32:E5:33 (xxxxxxxxxxxxxxx)
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: Trying to associate with 00:3a:98:32:8b:33 (SSID='xxxxxxxxxxxxxxx' freq=2462 MHz)
Aug  3 12:48:36 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  completed -> associating
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: Association request to the driver failed
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: CTRL-EVENT-DISCONNECTED - Disconnect event - remove keys
Aug  3 12:48:36 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associating -> disconnected
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: Associated with 00:3a:98:32:8b:33
Aug  3 12:48:36 stlinux wpa_supplicant[1617]: CTRL-EVENT-CONNECTED - Connection to 00:3a:98:32:8b:33 completed (reauth) [id=0 id_str=]
Aug  3 12:48:36 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  disconnected -> associated
Aug  3 12:48:36 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associated -> completed
Aug  3 12:48:41 stlinux NetworkManager: <debug> [1280857721.002375] periodic_update(): Roamed from BSSID 00:3A:98:32:E5:33 (xxxxxxxxxxxxxxx) to 00:3A:98:32:8B:33 (xxxxxxxxxxxxxxx)
Aug  3 12:50:15 stlinux wpa_supplicant[1617]: Trying to associate with 00:3a:98:32:e5:33 (SSID='xxxxxxxxxxxxxxx' freq=2437 MHz)
Aug  3 12:50:15 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  completed -> associating
Aug  3 12:50:16 stlinux wpa_supplicant[1617]: Association request to the driver failed
Aug  3 12:50:16 stlinux wpa_supplicant[1617]: CTRL-EVENT-DISCONNECTED - Disconnect event - remove keys
Aug  3 12:50:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associating -> disconnected
Aug  3 12:50:16 stlinux wpa_supplicant[1617]: Associated with 00:3a:98:32:e5:33
Aug  3 12:50:16 stlinux wpa_supplicant[1617]: CTRL-EVENT-CONNECTED - Connection to 00:3a:98:32:e5:33 completed (reauth) [id=0 id_str=]
Aug  3 12:50:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  disconnected -> associated
Aug  3 12:50:16 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associated -> completed
Aug  3 12:50:17 stlinux NetworkManager: <debug> [1280857817.001237] periodic_update(): Roamed from BSSID 00:3A:98:32:8B:33 (xxxxxxxxxxxxxxx) to 00:3A:98:32:E5:33 (xxxxxxxxxxxxxxx)
Aug  3 12:51:04 stlinux AptDaemon: INFO: Quiting due to inactivity
Aug  3 12:51:04 stlinux AptDaemon: INFO: Shutdown was requested
Aug  3 12:51:39 stlinux wpa_supplicant[1617]: CTRL-EVENT-DISCONNECTED - Disconnect event - remove keys
Aug  3 12:51:39 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  completed -> disconnected
Aug  3 12:51:39 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  disconnected -> scanning
Aug  3 12:51:40 stlinux wpa_supplicant[1617]: Trying to associate with 00:3a:98:22:a8:03 (SSID='xxxxxxxxxxxxxxx' freq=2412 MHz)
Aug  3 12:51:40 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  scanning -> associating
Aug  3 12:51:40 stlinux wpa_supplicant[1617]: Association request to the driver failed
Aug  3 12:51:41 stlinux NetworkManager: <debug> [1280857901.000191] periodic_update(): Roamed from BSSID 00:3A:98:32:E5:33 (xxxxxxxxxxxxxxx) to (none) ((none))
Aug  3 12:51:45 stlinux wpa_supplicant[1617]: Authentication with 00:3a:98:22:a8:03 timed out.
Aug  3 12:51:45 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associating -> disconnected
Aug  3 12:51:45 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  disconnected -> scanning
Aug  3 12:51:47 stlinux wpa_supplicant[1617]: Trying to associate with 00:3a:98:22:a8:03 (SSID='xxxxxxxxxxxxxxx' freq=2412 MHz)
Aug  3 12:51:47 stlinux wpa_supplicant[1617]: Association request to the driver failed
Aug  3 12:51:47 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  scanning -> associating
Aug  3 12:51:47 stlinux wpa_supplicant[1617]: Associated with 00:3a:98:22:a8:03
Aug  3 12:51:47 stlinux wpa_supplicant[1617]: CTRL-EVENT-CONNECTED - Connection to 00:3a:98:22:a8:03 completed (reauth) [id=0 id_str=]
Aug  3 12:51:47 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associating -> associated
Aug  3 12:51:47 stlinux NetworkManager: <info>  (wlan0): supplicant connection state:  associated -> completed