When you install RRAS on 2008 r2 server with IPv6 disabled inregistry (disabled components) RRAS likely will fail to start. My error message was
The Routing and Remote Access service terminated with service-specific error 31 (0x1F).
Unable to load C:WindowsSystem32iprtrmgr.dll.
What you need to do is:
Remove following key
Remove that, and try to start the service. Voila!