Once in a while on a server, you may notice the Microsoft Exchange Address Book service is not running. Attempting to start it manually results in the error:

Error
Unable to register the MSExchangeAB RPC interface. Failed with the error code The endpoint is a duplicate (1740)

What this message really is saying is that something else is already running on the same ports the Exchange service wants to use (6002/tcp to be precise).

To resolve the issue, use a command prompt and netstat -abo to figure out which process is holding onto port 6002/tcp. When found, you can then find a way to resolve the issue (e.g. by moving the service to another machine or by stopping it).

I found out  ...