hanging 7.12.UC3

The symptom is an Informix that has been running fine for days or weeks suddenly gets one or more network receive errors. Then a long checkpoint occurs that takes thousands of seconds instead of the normal 300 specified in CKPTINTVL in the onconfig file. All processes hang, and we're dead in the water. Usually either the checkpoint runs to completion after a half hour or more or the system halts itself We've got AFDEBUG turned on and will dump shared memory and check for the active session, thread, and sql running at the time this next happens. But has anyone else seen this kind of nasty hang? Thanks. --Stuart