You see the Post stopped with the following error in event log:
02/22/08 22:51 Process exited sp_opst (for o.SID1-o.SID2 queue queuename) [pid = 6901] - exit(1)
02/22/08 22:51 Internal error: 15013 - Error for que_reread() que_RRLS_SEQ: Readrelease sequence error [sp_opst (for o.SID1-o.SID2 queue queuename)/6901]
Can be caused by a number of things like the number of forward messages doesn't match backward one from the capture bug identified recently
1) The problem can happen (but is not limited to these) when there is a NOP rolled back at the start of a transaction, partial rollback issues, queue corruption, etc.
2) One quick workaround that can be tried is to start Post manually and see if it continues processing. If it did, there will be no harm done and the things will start moving once again.
