To set the mood for the upcoming error, remember on an earlier post, we had talked about replacing you Exchange 2003 Front-End server with an Exchange 2007 CAS server and we had also discussed that we could continue redirecting all incoming OWA requests to the /exchange virtual directory.

OK, so our OWA users in this example access their mailboxes via an Exchange 2007 CAS server, and everybody is redirected to the /exchange virtual directory. Mailboxes currently reside on both the Exchange 2003 and 2007 servers. When users with mailboxes on the Exchange 2007 server tried to login to OWA, this is what they saw:

Users with mailboxes on Exchange 2003 worked just fine, and if 2007 users connected to the /OWA virtual directory they were able to access their mailbox with no problems either. I started looking at the Exchange and ExchWeb virtual directories on the CAS server but they looked OK. Everything on the CAS looked OK actually. Anyhow, I looked at the services on the Exchange 2007 mailbox server and saw the World Wide Web Publishing service was not running. It figures, I started it back and Exchange 2007 users could once again access their mailboxes through OWA.