OWA 2010 Error: "The server operation timed out"

I was performing a small migration for Exchange 2007 to Exchange 2010. Because this migration was small, we didn't configure simultaneous access to owa on both platforms. Simultaneous access to owa on both platforms requires a second external IP and would have been too time consuming to bother with.

After migrating mailboxes to the new server, we could log on to owa, but when I accessed messages, we got the following error:

The server operation timed out. Please try again later.

A quick review of the owa configuration revealed that the owa on both Exchange 2007 and Exchange 2010 were using the same external URL. This was confusing the access to the messages.

After I removed the external URL from owa in Exchange 2007 the error was resolved and all was good.