Remote desktop - force log-off

Hello all,
We've met a problem using RDP: unable to force log-off the remote session. That means, when we, let's say, press "Escape" button on the remote host, the session is logged off, our server gets corresponding event

rdp.Disconnect(); 

and everybody is happy.
BUT sometimes we have to disconnect "by force". In this case, after

rdp.Disconnect()

the session is left open, and that's not good.
I found

rdp.Invoke()

method, but it gets function delegate as a parameter, and executing this function results in actions on the host and not on the remote one
We tried to call Shutdown.exe, but it can't logoff remote hosts (options "/l" and "/m //servername" cannot be used together).
 
So, there're two questions:
- How to close remote session ?
- How does rdp.invoke() works ?
Any help will be highly appreciated.
Julia.