OWA not working after upgrading to EV10

We have upgraded from EV 9.0.1 x32 to EV10 (2008 R2 Server) we can open archived emails from Outlook successfully, however not from OWA.

Receive error 'Remote server returned an error:(404) Not Found'

I have changed the server name in the evserver.txt file and ran the OWA 2003 Extension msi again then restarted IIS with no success.

We are using Exchange 2003

Please advise.