I have a similar symptom in karmic (9.10) 32 and 64 bit system using a DWL-G122 Rev. B1.
When I try to connect to the access point the protocol negotiation seems to work but I can't get an IP address. If I configure the stick manually I can't ping anywhere, not even to the AP. The USB-Adapter worked in Ubuntu 9.04 and 8.10 without any problems.
lsusb reads:
xxx@dimension-e521:~$ lsusb
Bus 002 Device 004: ID 0d8c:0006 C-Media Electronics, Inc. Storm HP-USB500 5.1 Headset
Bus 002 Device 003: ID 03f0:0517 Hewlett-Packard LaserJet 1000
Bus 002 Device 002: ID 413c:2003 Dell Computer Corp. Keyboard
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 007: ID 046d:c51a Logitech, Inc. MX Revolution/G7 Cordless Mouse
Bus 001 Device 008: ID 2001:3c00 D-Link Corp. [hex] DWL-G122 802.11g rev. B1 [ralink]
Bus 001 Device 003: ID 0409:0058 NEC Corp. HighSpeed Hub
Bus 001 Device 002: ID 0644:0200 TEAC Corp. 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

syslog shows:
Nov  9 20:19:16 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) complete.
Nov  9 20:19:16 dimension-e521 NetworkManager: <info>  Config: set interface ap_scan to 1
Nov  9 20:19:16 dimension-e521 NetworkManager: <info>  (wlan0): supplicant connection state:  scanning -> disconnected
Nov  9 20:19:16 dimension-e521 NetworkManager: <info>  (wlan0): supplicant connection state:  disconnected -> scanning
Nov  9 20:19:18 dimension-e521 wpa_supplicant[1362]: CTRL-EVENT-SCAN-RESULTS 
Nov  9 20:19:18 dimension-e521 wpa_supplicant[1362]: WPS-AP-AVAILABLE 
Nov  9 20:19:18 dimension-e521 wpa_supplicant[1362]: Trying to associate with 00:24:fe:05:45:41 (SSID='FRITZ!Box Fon WLAN 7270' freq=2457 MHz)
Nov  9 20:19:18 dimension-e521 wpa_supplicant[1362]: Association request to the driver failed
Nov  9 20:19:18 dimension-e521 wpa_supplicant[1362]: Association request to the driver failed
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  (wlan0): supplicant connection state:  scanning -> associating
Nov  9 20:19:18 dimension-e521 kernel: [ 3331.669709] wlan0: authenticate with AP 00:24:fe:05:45:41
Nov  9 20:19:18 dimension-e521 kernel: [ 3331.672468] wlan0: authenticated
Nov  9 20:19:18 dimension-e521 kernel: [ 3331.672473] wlan0: associate with AP 00:24:fe:05:45:41
Nov  9 20:19:18 dimension-e521 wpa_supplicant[1362]: Associated with 00:24:fe:05:45:41
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  (wlan0): supplicant connection state:  associating -> associated
Nov  9 20:19:18 dimension-e521 kernel: [ 3331.688507] wlan0: RX AssocResp from 00:24:fe:05:45:41 (capab=0x431 status=0 aid=1)
Nov  9 20:19:18 dimension-e521 kernel: [ 3331.688514] wlan0: associated
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  (wlan0): supplicant connection state:  associated -> 4-way handshake
Nov  9 20:19:18 dimension-e521 wpa_supplicant[1362]: WPA: Key negotiation completed with 00:24:fe:05:45:41 [PTK=CCMP GTK=TKIP]
Nov  9 20:19:18 dimension-e521 wpa_supplicant[1362]: CTRL-EVENT-CONNECTED - Connection to 00:24:fe:05:45:41 completed (reauth) [id=0 id_str=]
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  (wlan0): supplicant connection state:  4-way handshake -> group handshake
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  (wlan0): supplicant connection state:  group handshake -> completed
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  Activation (wlan0/wireless) Stage 2 of 5 (Device Configure) successful.  Connected to wireless network 'FRITZ!Box Fon WLAN 7270'.
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 3 of 5 (IP Configure Start) scheduled.
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 3 of 5 (IP Configure Start) started...
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  (wlan0): device state change: 5 -> 7 (reason 0)
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  Activation (wlan0) Beginning DHCP transaction (timeout in 45 seconds)
Nov  9 20:19:18 dimension-e521 dhclient: Internet Systems Consortium DHCP Client V3.1.2
Nov  9 20:19:18 dimension-e521 dhclient: Copyright 2004-2008 Internet Systems Consortium.
Nov  9 20:19:18 dimension-e521 dhclient: All rights reserved.
Nov  9 20:19:18 dimension-e521 dhclient: For info, please visit http://www.isc.org/sw/dhcp/
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  dhclient started with pid 4066
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP6 Configure Get) scheduled...
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 3 of 5 (IP Configure Start) complete.
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP6 Configure Get) started...
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP6 Configure Get) complete.
Nov  9 20:19:18 dimension-e521 dhclient: 
Nov  9 20:19:18 dimension-e521 NetworkManager: <info>  DHCP: device wlan0 state changed normal exit -> preinit
Nov  9 20:19:18 dimension-e521 dhclient: Listening on LPF/wlan0/00:11:95:ca:d1:9c
Nov  9 20:19:18 dimension-e521 dhclient: Sending on   LPF/wlan0/00:11:95:ca:d1:9c
Nov  9 20:19:18 dimension-e521 dhclient: Sending on   Socket/fallback
Nov  9 20:19:22 dimension-e521 dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 3
Nov  9 20:19:25 dimension-e521 dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 3
Nov  9 20:19:28 dimension-e521 dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 5
Nov  9 20:19:33 dimension-e521 dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 11
Nov  9 20:19:44 dimension-e521 dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 12
Nov  9 20:19:56 dimension-e521 dhclient: DHCPDISCOVER on wlan0 to 255.255.255.255 port 67 interval 10
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  (wlan0): DHCP transaction took too long, stopping it.
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  (wlan0): canceled DHCP transaction, dhcp client pid 4066
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP4 Configure Timeout) scheduled...
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP4 Configure Timeout) started...
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  (wlan0): device state change: 7 -> 9 (reason 5)
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  Activation (wlan0) failed for access point (FRITZ!Box Fon WLAN 7270)
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  Marking connection 'Auto FRITZ!Box Fon WLAN 7270' invalid.
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  Activation (wlan0) failed.
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  Activation (wlan0) Stage 4 of 5 (IP4 Configure Timeout) complete.
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  (wlan0): device state change: 9 -> 3 (reason 0)
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  (wlan0): deactivating device (reason: 0).
Nov  9 20:20:04 dimension-e521 NetworkManager: <info>  Policy set 'Auto eth0' (eth0) as default for routing and DNS.
Nov  9 20:20:04 dimension-e521 kernel: [ 3377.585105] wlan0: disassociating by local choice (reason=3)
Nov  9 20:20:04 dimension-e521 wpa_supplicant[1362]: CTRL-EVENT-DISCONNECTED - Disconnect event - remove keys
Nov  9 20:20:35 dimension-e521 wpa_supplicant[1362]: CTRL-EVENT-SCAN-RESULTS 

If I can be any help pleas let me know.