According to Microsoft this problem can occur when the wrong context pointer is passed to an ISAPI filter. See ME899472
for a hotfix applicable to Microsoft IIS 5.0.
This event also appears after running iisreset.exe.
See the link to "Symantec Support Document ID:2004040209303954" for details on this event.
This event is closely related to the Code Red Worm or one of it's variants. One of my servers was infected with the worm and exhibited this event in the logs numerous times. Upon clearing out the worm, the events have stopped. This event was coupled with another very similar event stating that the service was being issued a "start" command. There were also events about all of the web services, (web, ftp, smtp) terminating unexpectedly that occurred in the same time frame. If you are seeing these events together, they indicate you are infected.