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Exchange Connection Problems? Check This Registry Key

After I performed an over-the-top reinstall of Windows 2000 Professional on a user's PC, the user was having connection problems with Microsoft Exchange Server. When I called Microsoft Product Support Services (PSS), an Exchange-savvy representative pointed me to the articles "XCLN: RPC Ping Utility and Exchange 2000 Server" ( and "XCLN: How to Use RPCPing to Test RPC Communication ( However, before I even read the articles, he had me check the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\ClientProtocols registry key for the following entries and values:

  • ncacn_np = rpcrt4.dll
  • ncacn_ip_tcp = rpcrt4.dll
  • ncadg_ip_udp = rpcrt4.dll
  • ncacn_nb_tcp = rpcrt4.dll
  • ncacn_http = rpcrt4.dll

The user's machine was missing these entries and values. The PSS representative provided a .reg file with this information, which I then imported into the problematic machine. The Exchange server was then immediately available for connection in the user's email profile.

Six months later, I had to perform the simple task of moving a customer's PC from one domain to another. To maintain the customer's desktop and assorted preferences, I chose to disjoin the PC from the existing domain to a Windows workgroup, then change from the workgroup to the new domain. I accomplished this task by right-clicking MyComputer, selecting Properties, choosing the Computer Name tab, and clicking Change. (Incidentally, I'm aware of the Moveuser utility, but that utility doesn't move a profile from domain to domain.)

I thought all had gone well until the customer called me a couple hours later and said, "I have no emails or contacts anymore." He still had access to some shared folders on the Exchange server, so I knew the network was okay. I checked Exchange System Manager (ESM) for orphaned mailboxes but found none. The Exchange server didn't move. It was still in the same domain it had always been in. I then checked the Microsoft Management Console (MMC) Active Directory Users and Computers snap-in's Exchange tabs for the customer's account in the new domain. The information on those tabs looked correct as well. Two hours have passed and I'm thinking, "I've smelled this problem before." I pulled out my "toolbox CD" and looked in my Exchange Server folder. There was the .reg file I had used 6 months prior to fix the user's machine.

So, I browsed to the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Rpc\Client Protocols registry key on the customer's PC. Sure enough, the five entries and their values were missing. I imported the .reg file and, once again, the Exchange connection problem was immediately resolved.

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