RPC by default can grab any dynamic port above 1024.  Security sometimes may ask you to limit that to a much narrower range.  A the minimum you should have about 100-200 ports available for RPC communication.

Here is the registry setting:

HKEY_LOCAL_MACHINE\Software\Microsoft\Rpc

Ports: REG_MULTI_SZ: 5000-5100

PortsInternetAvailable: REG_SZ: Y

UseInternetPorts: REG_SZ: Y

 

Full MS KB