Well, I have done everything that you advised with the 2005 files but I still get the Runtime Message as soon as I try to go to a FSDT airport, GSX worked fine until I was advised an update was available via Live Update.
I ran the live update and thats when this problem started. I fail to see how the problem can be caused by FSX or Windows 7 and to re-install either program on the off chance of curing this problem seems a bit extreme to say the least, it looks as if I wasted my money and I will have cut my losses and sadly abandon GSX.