Assert failure

Before phoning Tech Support, is there anyone here that can tell me more about this error I received: Is there anything specific I can look for in the af-file to try and troubleshoot this myself ? I can see it was caused by sessionid 5722, from user "tad" - any pointers / tips ? I found the last sql statement executed by this session, and ran onchecks on the tables in this statement, but found nothing abnormal. Oncheck -cr and oncheck -cc is also fine. My system has been stable for 3 years, now suddenly this. There are no messages at all in the Unix messages file. 14:40:55 Assert Failed: No Exception Handler 14:40:55 Informix Dynamic Server Version 7.31.FD3 14:40:55 Who: Session(5722, tad@mxctrl, -1, 1197344144) Thread(5136, sqlexec, 348b236c8, 3) File: mtex.c Line: 454 14:40:55 Results: Exception Caught. Type: MT_EX_OS, Context: mem 14:40:55 Action: Please notify Informix Technical Support. 14:40:56 Assert Failed: No Exception Handler 14:40:56 Informix Dynamic Server Version 7.31.FD3 14:40:56 Who: Session(25151, tad@mxctrl, -1, 1033926344) Thread(24605, sqlexec, 348b22908, 5) File: mtex.c Line: 454 14:40:56 Results: Exception Caught. Type: MT_EX_OS, Context: mem 14:40:56 Action: Please notify Informix Technical Support. sending to informix-list