I work for a school that uses over a dozen Aironet 1100 access points to provide Wifi access across campus. We have two networks, one for students and one for teachers, each with hidden SSIDs and WPA-PSK authentication. We're running into an issue where Mac laptops running OS 10.5-10.6 will randomly lose their stored profile for our network, usually after sleep or reboot. When the problem occurs all records of our network are missing from the airport menu and the network system preference pane. We've tried using different locations in the Network PrefPane, removing locations and setting it to the 'automatic' location and it has no effect.
The issue seems to be isolated to corruption of a .plist file stored in /Library/Preferences/SystemConfiguration as deleting said .plist files will temporarily resolve the issue. However in many cases the symptom returns after the computer goes to sleep or after a reboot. I would think the issue is isolated to the Mac OS but none of the users have similar issues connecting to other access points at other locations.
I've contacted Apple support and as of yet they have no idea what may be occuring here and suggested I contact Cisco.
On the Cisco side we've tried resetting several of the access points to see if the frequency of the symptom changes. So far resetting the APs appears to have not effected the symptom.