This problem is due to Cisco bug ID CSCsg21262. The exact error message is as follows:
Date time 00:00:00:00:00:00 Invalid Session Id 320868138 in message from AP 00:00:00:00:00:00 Date time 00:00:00:00:00:00 Failed decryption of message from AP 00:00:00:00:00:00 Date time 00:00:00:00:00:00 Security processing of Echo Request failed from AP 00:00:00:00:00:00
The problem is first found in these versions:
It is fixed in version 4.0(206). The error message indicates that there is an issue with the key rotation for the AP. The new code for the 4.0 train is released. The code is 22.214.171.124(For Registered Users Only). Upgrade to this version in order to resolve the problem.
These additional Cisco bug IDs relate to a similar problem: