Whs Remote Access (Rdp) Woes

I am trying to get remote desktop to work consistently, primarily so I can use it to access computers at home when I am on the road - I do this through Windows Home Server. Here's a brief summary:



I have four computers on a workgroup (NOT a homegroup) called 'RACECAR', as follows:

• Aston-Martin: laptop running Win7 Pro
• Jaguar: desktop running XP Pro SP3
• Mirage: headless server running Windows Home Server
• Ferrari: desktop running Win7 Pro, upgraded from Home Premium with Anytime upgrade.

All machines are connected by Cat6 Ethernet and a gigabit switch to a Draytek router and thence to the ISP.

I can attempt login to any computer from any other in one of two ways:

• Remote Desktop Connection (MSTSC)
• Home server remote access (https://<mydomain>.homeserver.com)

Here's the problem:

• I can access Aston-Martin, Jaguar and Mirage from any of the other computers using either 1 or 2
• I can also access any machine FROM Ferrari
• Ferrari shows up in Windows Explorer, and I can copy and paste files to and from it
• Ferrari shows as 'available for connection' in the WHS remote access 'Computers' list
• I cannot access Ferrari from any other machine. I receive the message:
  
  "Remote Desktop can't connect to the remote computer for one of these reasons:
  
  1) Remote access to the server is not enabled
  
  2) The remote computer is turned off
  
  3) The remote computer is not available on the network
  
  Make sure the remote computer is turned on and connected to the network, and that remote access is enabled."

As an experiment, I tried using Remote Assistance between Aston-Martin and Ferrari. This works in both directions, in that I can see the remote machine's desktop - though not control it with the keyboard.

I have port 3389 open in the firewall (Windows Firewall), and have set the relvant permissions in the Remote tab of Properties.

I have tried Ferrari both using a computer name, and also the IP address on the LAN, with a qualifying port number. Doesn't make any difference, fails either way.

I'm wondering if the problem is to do with the fact that the machine was upgraded, rather than having an original copy of 7 Pro (I know remote access is one of the limitations of HP). Anyway, I am really at my wits' end with this, and can't find any obvious pointers on the web. If anyone has any thoughts, they would be very much appreciated.