Crickets. Is there anyone out there? I have tried talking to Genius Bar, Macology and Microsoft and no one seems to know what the problem is. How can this be. The issue isn't just with Microsoft's Remote Desktop Connection for Mac. I now can't connect with CoRD, either. Maybe it's a Windows 7 issue? There were about 500 different exceptions available. I created the recommended exception for Remote Desktop.
I can't answer your problem, but maybe can provide some color commentary.
I use the RDP from Microsoft too and it has been working very well. Recently, though, I've only been able to connect to my work Windows computer (XP Pro) ONE TIME. After I exit RDP, then I can't connect to my work computer.
In fact, I can't even PING my work computer after I disconnect which I find a bit odd. After I have a co-worker (who is going to start ignoring my calls) reboot, all works fine. I have a workaround, I'll simply reboot my computer JUST BEFORE logging out.
I'm using Cisco VPN on Macbook. Perhaps our problems are similar.