I think it might be problem with some level in the communication between the AP and the authentication server. Verify that you can ping from the Access Point (AP) to the server. For more information, refer to the Performing Pings and Link Tests section of Cisco Aironet 1200 Series Network Management. Check your network to make sure that traffic between the two devices is not blocked by any intervening firewall or traffic filters. If there is good IP connectivity, reset the shared keys (shared secrets) on the AP and the server to ensure they match.