I had the same problem
described here, changing the wireless mode on the access point from b&g to just b has sorted the problem out.
I still howerver have some difficulty with this:
Jan 31 23:51:53 wpa_supplicant[361]: WPA: Group rekeying completed with 00:1b:2f:48:61:02 [GTK=TKIP]
Jan 31 23:52:07 wpa_supplicant[361]: CTRL-EVENT-SCAN-RESULTS
Jan 31 23:57:10 wpa_supplicant[361]: CTRL-EVENT-SCAN-RESULTS
Feb 1 00:02:13 wpa_supplicant[361]: CTRL-EVENT-SCAN-RESULTS
Every 30 minutes group rekeying completed turns up and I seem to loose connectivity briefly but annoyingly.