OWA will not allow users to get emails.

Exchange 5.5
IIS 4.0
NT 4.0

Getting Emails through OWA is very inconsistent. When it stops working, checking the management console shows the web has “stopped”. It can be restarted but won’ work until the World Wide Web Publishing Service has been stopped and restarted. Then, messages can be accessed through IE. This access can vary between 5 minutes and 1 hour before the web stops again. No changes have been made to the server. Both Exchange and IIS are running on the same server and have been for 4 years with very little problem.