It sounds like a firewall is blocking the download of support.txt file - ZoneAlarm for example gave me this error but I allowed the application past and there was no issue. Let us know Martin
I have the same problem and I found a solution. I download http://designspark.eu/data/support.txt on my computer and i replace "http://designspark.eu/data/" in the message box by the address of my download folder.
I have found a workaround. When I run DesignSpark PCB under elevated permissions (Right-click on DesignSpark and click Run as Administrator), the ModelSource window is able to connect and works fine. But this is not a great solution of the problem, I want to be able to run the software with normal user rights.