If a reboot makes the unit work for a while, try upgrading the firmware to the most recent; there is also a beta image that's not released yet that fixes the issue of APs locking up.
Use a serial cable to console to the AP and reboot it. Watch the post messages that come up. "failure to load awc0 driver, or somesuch, means you likely have corrupted firmware and would have to send the unit back to the factory.
If you can, you can try defaulting the config, and reflashing the firmware; sometimes this works.
Transferring Crash file from standby: Login to the Active WLC in HA.
From CLI: (Cisco Controller) >transfer upload datatype crash (Cisco
Controller) >transfer upload filename (Cisco
Controller) >transfer upload mode tftp (Cisco Controller) >transfer
This is the start of a display filter cross reference between Wireshark
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