I've no doubt this question has probably been asked before so I apologise in advance if I am doubling up!

Can anyone give a list of the definitive services required to be active / disabled on a remote PC in order to avoid this response:

The RPC server is unavailable. (Exception from HRESULT: 0x800706BA)
The machines in question are behind an enterprise firewall, as is the host, so Windows Firewall is turned off.

Remote Procedure Call (RPC) - auto
Remote Registry - auto
Windows Remote Management (WS-Management) - auto
Windows Management Instrumentation - auto

These are the obvious enabled services, but I can not get an answer from any Microsoft website as to what needs to be set for remote administration.
The error code seems to be very general, with lots of reasons for it. Not all related to remote access.
Currently, with the above set, some Windows 7 machines work and some don't, hence my confusion.

Any thoughts would be appreciated.