Assume that you apply Update Rollup 1 for Microsoft Exchange Server 2010 Service Pack 2 on an Exchange Server 2010 Client Access server. The Exchange Server 2010 Client Access server acts as a proxy server for an Exchange Server 2007 Client Access server that is not connected to the Internet. When a user tries to log on to Outlook Web App (OWA) in this situation, the logon attempt fails. Additionally, you receive an error message that states that an exception was thrown on the proxy server.
Note This issue may also occur when the proxy is set up between Exchange Server 2010 Client Access servers, and not all the servers are updated.