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Exchange RPC over HTTP Stopped Working

I have a single Exchange 2003 SP2 server with one Outlook client connecting via RPC over HTTP.  After working for several weeks without a hitch it stopped working - The Outlook client cannot connect.  Nothing has changed on my firewall and I did not modify anything in the Exchange server during the period in which it failed.  There are no obvious errors in the system logs.

In the document I used to set up RPC over HTTP with a single Exchange server (no back-end/front-end stuff), it tells you to test it by going to http://your.server's.FQDN/rpc, authenticating with "domain\username."  You are supposed to get an error that says "This page cannot be displayed.  HTTP Error 403.2 - Forbidden: Read access is denied" as a confirmation that RPC is working, but instead it keeps asking me for my username and password.  I went back through the entire document to verify that all the setting are still as they had been configured and they are.

Any guidance on how to troubleshoot this would be appreciated.
1 Solution
This link will help you troubleshoot the issue: http://go.microsoft.com/fwlink/?LinkId=66192

For troubleshooting problems associated with connectivity it is often advisable to disable the protocol failback.  When Outlook 2003 cannot make an RPC over HTTP connection it will atuomatically use the TCP/IP protocol to make an RPC over MAPI connection.  To do this modify the following key in the registry


Create an entry DisableRpcTcpFallback and set it to the DWORD value of 1.  To reauthorize fallback you can set this value to 0.

You may also wish to enable Outlook 2003's RPC tracing.  You configure this under Tools | Options | Other | Advanced Options.  Ensure the Mail Logging (troubleshooting) checkbox is enabled.  With this enabled (after restarting Outlook) Outlook will write events to the machines Application log.

If this tracking is insufficient you can alternately enhance this through creating some additional registry entries and replacing certail .dll files on the client.  Under the HKEY_CURRENT_USER\Software\Microsoft\Office\11\Outlook\RPC subkey create the following entries:  RpcTraceEnable, RpcStackTrace,RpcDumpToFile, and RpcOutputDir.  Additionally you will need to obtain new versions of the following dlls from Microsoft.  emsmdb32.dll, emsabp32.dll, emsui32.dll, and smsapi32.dll.

Finally you are likely to achieve much better performance when you change the RPC binding order to look first to the TCP/IP stack.  To do this modify the following registry key:


Change the Rpc_Binding_Order to ensure that ncacn_ip_tcp is listed before the other entries, including ncalrpc

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