I VPN into my work Windows PC (Win7) and used to use MS RDC to access it, but a little while ago a network move at work led to RDC no longer working.
The RDP connection via CoRD still works fine. On attempting to connect with Microsoft RDC 2.1 or 2.0.1, I get 2 error dialogs now. The first complains "The certificate is not from a trusted certification authority", whilst the second says that "The remote computer is not allowing connections from the Mac". Eeven though I have set the remote computer in question up to allow RDP, as evidenced by my ability to access it via CoRD.
I can still access other PCs on the same work network using RDC, just not the one I want to use. I'd prefer to use RDC over CoRD simply because it is faster on my 10.6.8 MacBook Pro.