Outlook Web Access

Periodically, say every two to five days our Outlook Web Access stops working. I have found that on the Exchange 5.5 Server, in Internet Service Manager (NT 4.0 Option Pack, under Internet Information Server)the two services for the Default Web Site and the Administration Web Site have stopped. When I manually start the two services, OWA works fine.

I have tested to see if our antivirus or Backup software, Inoculate IT & ArcServe IT 6.61 stop the services when they are run. In addition, I tested to see if the services stop once somebody accesses the Exchange Server through OWA. However, none of the above seems to stop the services. Any possible solutions?

Thanks,
Dan