I have a client using Exchange 2013 (CU 7) and we have been unable to get their OWA working. When we attempt to access the url we get the authentication page as expected, however when we log in with any user credential we get a "HTTP 400 Bad Request" message. I have confirmed that OWA is enabled for our users and used other browsers with the same result.
This has been tested only on the local lan as we don't want OWA accessible from outside the network.
Any suggestions you can offer would be much appreciated.