Problem with IIS 4.0

I have an intranet NT 4.0 server with SP5 running IIS 4.0. The server locks up the “WWW Publishing Service” almost every three weeks. I have to reboot the server to get it back online. Everytime when it locks up, Event Viewer shows “Event ID: 5. Source: Active Server Pages. Error: File /*.asp Unexpected error”. Anyone knows how to fix it?