Alternative RDP Port using Cisco ASA 5505

I have a Cisco ASA 5505 that I have NAT Access rules setup for RDP using port 3389.  I have port 3389 tied to a workstation on the network at 192.168.1.199.  I have one static IP address and this senario works great!  I need to setup RDP for another user to connect remotely also, but I only have one static IP.  So edited the registry on the other PC to use port 3390 for the listening port for RDP.  When I put in the static ip address XXX.XXX.XXX.XXX:3390 I cannot connect to the PC from a remote location.  I have the NAT Rules setup exactly like the rule for 3389/RDP.  I know that it is definitely a problem on the Cisco because I can RDP to XXX.XXX.XXX.XXX:3390 on the local network.

Any ideas what else I need to do?

Thanks,

Shawn