Remote Access to SBS2003 Server using the Remote Website provide

I have a Small Business Server 2003 setup in my office and I have been trying to get the Remote Desktop working from the webpage but it keeps failing

Here is the setup in my office

Small business server (192.168.0.1)
5 Client (DHCP Scope 192.168.0.10-20)
2 Network Printers (192.168.0.30-192.168.0.31)
Firewall (192.168.0.253) “Symantec Firewall / VPN 100”
Ports 80,443 & 3389 are all setup to forwarded to 192.168.0.1

I can connect using https://x.x.x.x/remote from remote locations, once in I am able to view email and server stats etc.  

But when I go into ‘Connect to Server Desktops’ I get the list of servers, so I select the server (which has had port 3389 setup to forward to) and it then starts to try and connect then fails with the following error :

The Client could not connect to the remote computer.  Remote connections might not be enabled or the computer might be too busy to accept new connections.  It is also possible that network problems are preventing your connection.  Please try connecting again later.  If the problem continues to occur, contact your administrator

So I then close internet explorer and try using the RDC Client, it works first time.  So my question is this, why does RDC Client work but not from the webpage? Has anybody else had this problem or got some ideas why it might not be working.