Comment 7 for bug 62106

I got the same issue with an Allied Telesyn PCMCIA card:

sudo lspci -v

03:00.0 Ethernet controller: Atheros Communications, Inc. AR5212 802.11abg NIC (rev 01)
Subsystem: Allied Telesyn International Unknown device 1204
Flags: bus master, medium devsel, latency 168, IRQ 11
Memory at f4000000 (32-bit, non-prefetchable) [size=64K]
Capabilities: [44] Power Management version 2

The workaround is available with the Mad Wifi tools installed :

sudo apt-get install madwifi-tools

ifconfig ath0 down
wlanconfig ath0 destroy
wlanconfig ath0 create wlandev wifi0 wlanmode [sta|adhoc|ap|monitor|wds|ahdemo]

Source of the workaround:

http://madwifi.org/wiki/UserDocs/ChangingMode

Hope this helps.