Recently, our Port forwarding for RDP seemed to stop working. Checking the firewall (Cisco ASA551), I can see the the NAT and access rules are configured correctly. In trying to connect from WIN7 to either a WIN7 or WINXP host, the firewall logs show the packet being passed, but no response is ever received on the client end.
In trying to diagnose the problem, I discovered that everything works perfectly fine from PocketCloud (a 3rd party Android RDP client).
I have verified the Server Authentication issues on the client RDP are set to "warn me". Internally, everything works as expected.