We have two 2010 SP1 CAS servers behind a Kemp load balancer using SSL offloading. OWA works fine. Autodiscover seems to set up Outlook 2010 clients fine. Users can set OOF in OWA. When users try to set OOF in Outlook 2010, they get the error, "your automatic reply settings cannot be displayed because the server is currently unavailable. Try again later". If I run the Outlook connectivity tests, it returns the internal URL that it is set for OOF (EWS). If I put that address into a web browser, it prompts for credentials, then returns the expected xml data. I also get the following error in the event log. Source:System.ServiceModel 3.0.0.0 Event ID: 3 Description: WebHost failed to process a request. Sender Information: System.ServiceModel.ServiceHostingEnvironment+HostingManager/30542218 Exception: System.ServiceModel.ServiceActivationException: The service '/EWS/Exchange.asmx' cannot be activated due to an exception during compilation. The exception message is: A binding instance has already been associated to listen URI 'http://CAS1/EWS/Exchange.asmx'. If two endpoints want to share the same ListenUri, they must also share the same binding object instance. The two conflicting endpoints were either specified in AddServiceEndpoint() calls, in a config file, or a combination of AddServiceEndpoint() and config. I ran through all the suggestions in http://social.technet.microsoft.com/Forums/en-US/exchange2010/thread/b5026be0-c7ef-4fc2-878c-cd80f2ee26c8?prof=required as well as a few others I found on the net. I stopped short of reinstalling the CAS role. I have tried changing the Authorization levels in IIS and rebooting each time. (iisreset /noforce times out so a reboot seemed necessary) I've tried every combination of Anonymous, Basic, and Windows authentication that I can think of. I have removed the Web services virtual directory and recreated it through EMS. I have reset both EWS and Autodiscover through EMC. I can provide any other information to help solve this.

So, you have tried to recreate the /EWS virtual directory, right? I assume that you have verified the permissions, right? Default settings for Exchange-related virtual directories in Exchange Server 2010 Does anything else between the CAS servers and the clients except the Kemp load balancer, like TGM server? Please try to bypass the load balancer, let the client to contact the CAS servers directly, see if the issue still appears Have you modified the Web.Config file on the CAS servers before? The similar symptom can appear if the file has been changed incorrectly. Please backup the original Web.Config file, replace it with a copy from a working lab, and then check the issue again James Luo TechNet Subscriber Support in forum If you have any feedback on our support, please contact tngfb@microsoft.com Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.