We are using a Dell Vostro i5 with 8GB memory and server 2008R2.
I think I was misunderstood.

Or, possibly I don't understand.

The only thing I know for sure now is there is a T110 with Server 2008 R2 and a Dell Vostro with Server 2008 R2 being used as a TS.
My only suggestion as a trial would be to turn on the Remote Desktop Services role on the server OS (which at the moment has no reason to be on, correct?) and see if it works that way.
Also, keep in mind, that there have been times I have received that same error, which had nothing to do with a TS. Haven't seen it in months.