Same problem here with Atheros AR5001X+ and Ubuntu Jaunty (amd64) Stable.

1 - Click on NetworkManager icon
2- Create new Wireless Network
3- Name: Net (no encription)

module -> ath5k

/var/log/syslog

May  3 00:12:52 sistematico NetworkManager: <info>  Activation (ath0) starting connection 'Net' 
May  3 00:12:52 sistematico NetworkManager: <info>  (ath0): device state change: 3 -> 4 
May  3 00:12:52 sistematico NetworkManager: <info>  Activation (ath0) Stage 1 of 5 (Device Prepare) scheduled... 
May  3 00:12:52 sistematico NetworkManager: <info>  Activation (ath0) Stage 1 of 5 (Device Prepare) started... 
May  3 00:12:52 sistematico NetworkManager: <info>  Activation (ath0) Stage 2 of 5 (Device Configure) scheduled... 
May  3 00:12:52 sistematico NetworkManager: <info>  Activation (ath0) Stage 1 of 5 (Device Prepare) complete. 
May  3 00:12:52 sistematico NetworkManager: <info>  Activation (ath0) Stage 2 of 5 (Device Configure) starting... 
May  3 00:12:52 sistematico NetworkManager: <info>  (ath0): device state change: 4 -> 5 
May  3 00:12:52 sistematico NetworkManager: <info>  Activation (ath0/wireless): connection 'Net' requires no security.  No secrets needed. 
May  3 00:12:52 sistematico NetworkManager: <info>  Config: added 'ssid' value 'Net' 
May  3 00:12:52 sistematico NetworkManager: <info>  Config: added 'mode' value '1' 
May  3 00:12:52 sistematico NetworkManager: <info>  Config: added 'frequency' value '2412' 
May  3 00:12:52 sistematico NetworkManager: <info>  Config: added 'key_mgmt' value 'NONE' 
May  3 00:12:52 sistematico NetworkManager: <info>  Activation (ath0) Stage 2 of 5 (Device Configure) complete. 
May  3 00:12:52 sistematico NetworkManager: <info>  Config: set interface ap_scan to 2 
May  3 00:12:52 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  scanning -> disconnected 
May  3 00:12:52 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  disconnected -> scanning 
May  3 00:12:52 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  scanning -> associating 
May  3 00:13:02 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  associating -> disconnected 
May  3 00:13:02 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  disconnected -> scanning 
May  3 00:13:02 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  scanning -> associating 
May  3 00:13:08 sistematico NetworkManager: <info>  ath0: link timed out. 
May  3 00:13:12 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  associating -> disconnected 
May  3 00:13:12 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  disconnected -> scanning 
May  3 00:13:12 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  scanning -> associating 
May  3 00:13:22 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  associating -> disconnected 
May  3 00:13:22 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  disconnected -> scanning 
May  3 00:13:22 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  scanning -> associating 
May  3 00:13:28 sistematico NetworkManager: <info>  ath0: link timed out. 
May  3 00:13:32 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  associating -> disconnected 
May  3 00:13:32 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  disconnected -> scanning 
May  3 00:13:32 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  scanning -> associating 
May  3 00:13:42 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  associating -> disconnected 
May  3 00:13:42 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  disconnected -> scanning 
May  3 00:13:42 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  scanning -> associating 
May  3 00:13:48 sistematico NetworkManager: <info>  ath0: link timed out. 
May  3 00:13:52 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  associating -> disconnected 
May  3 00:13:52 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  disconnected -> scanning 
May  3 00:13:52 sistematico NetworkManager: <info>  (ath0): supplicant connection state:  scanning -> associating 
May  3 00:13:53 sistematico NetworkManager: <info>  Activation (ath0/wireless): association took too long, failing activation. 
May  3 00:13:53 sistematico NetworkManager: <info>  (ath0): device state change: 5 -> 9 
May  3 00:13:53 sistematico NetworkManager: <info>  Activation (ath0) failed for access point (Net) 
May  3 00:13:53 sistematico NetworkManager: <info>  Marking connection 'Net' invalid. 
May  3 00:13:53 sistematico NetworkManager: <info>  Activation (ath0) failed. 
May  3 00:13:53 sistematico NetworkManager: <info>  (ath0): device state change: 9 -> 3 
May  3 00:13:53 sistematico NetworkManager: <info>  (ath0): deactivating device (reason: 0). 
May  3 00:13:53 sistematico NetworkManager: <info>  Policy set 'Claro' (ppp0) as default for routing and DNS.