I too am having this issue, I am running a WiSM with 22.214.171.124. The AP will connect then say %CAPWAP-3-ERRORLOG: Retransmission count for packet exceeded max(CAPWAP_ECHO_REQUEST) and reboot.
Was suggested by TAC to do two simatanious captures. That's interesting to setup with a all Fiber 6500 and no copper available. Come on, there has to be something to this. I have been reading this same issue all over the place. My AP is one switch away from my core, no interface drops or errors, and the AP is dropping 5 packets and the AP goes POOF?