We have OWA running on a front-end server in our DMZ, connecting to one back-end server and both running Exchange 2003 SP2. Periodically, OWA stops functioning but no services stop on either server, and all other mail flow is unaffected. The only way to get OWA working again is to reboot the back-end server. The server logs show no issues, and the IIS logs only show 500 errors when users attempt to login after OWA stops working. This is a random occurence, happening twice in the past 3 months, but only once before that in the past year. Any help would be greatly appreciated.