[strongSwan] Any special settings for RDP over a Strongswan IPsec VPN?

[Lawrence Chiu]

Have a working Strongswan IPsec VPN set up but can't seem to get RDP 
working.  Over VPN, the remote client can browse the Internet, intranet, 
FTP, Windows shares, etc.  But open an RDP session and get a black 
screen and eventually (after 20 seconds or so) the error:

"Your Remote Desktop Services session has ended.
The connection to the remote computer was lost, possibly due to network 
connectivity
problems. Try connecting to the remote computer again.  If the problem 
continues, contact
your network administrator or technical support.
[OK] [Help]"

Are there any special settings that are required to get RDP to work?  
Thanks!