The Error I was getting from OWA was one I have found all over the internet, but was unable to use any solution provided to fix it. When I tried to log into OWA I received a screen that said:
Outlook Web Access could not find a mailbox for EXCHANGE0\IUSR_HOST. If the problem continues, contact technical support for your organization and tell them the following: The mailbox may be stored on a Microsoft Exchange 2000 or Microsoft Exchange 2003 server, or the Active Directory user account was created recently and has not yet replicated to the Active Directory site where this Client Access server is hosted.
As you can read above, I found that my ServerName was the old server that I had migrated from. OWA would not log me, or any oof my users, in because there was no mailbox on that server according to the server name.
What solved my problem was to disable the mailbox then re-connect it. After connecting, my server was listed as the correct servername and I am able to log onto OWA.
I hope this will help someone else.