The first encrypted message sent by either party is the Finished message, seen here as the "Handshake" message at 363 8. The alert essentially means that the server (F5) was unable to decrypt this message and/or verify its mac (ie. signature). Unfortunately there's a few different reasons for this event to occur, including a bad client or server crypto implementation, bad server public or private key, and potentially any network issues that could have corrupted some part of the previous handshake.
Have you been able to isolate and reproduce this error?