I'm not an expert, but I'll give you my 2 cents and maybe it will help.

I just upgraded the program to 6.6 and installed it on my 64 bit Vista machine. To avoid future access priviledge problems I installed it in a different directory than under Program Files. In my case, apps\gstudio. I installed as admin as well. So far all seems to work fine.

Of course first make sure you have a non-corrupt copy of the program and update by redownloading.

Good luck,
Keith