I cannot promise to be of much assistance tracking the root of the problem, but I think anyone is going to want the following to be specified before they can help you;
1. Is the build of the program that works on your friends' computer an executable, compiled on your computer, that you have given them? Or is it your code compiled on their respective computers with their own installations of A5?
2. Are they all using Win 7 x64?
3. Post the code, and perhaps an executable compiled on your comp, too, if the site allows that.
I have Win 7 / x64 as an alternate OS on my second computer. Don't use it much at all (Win 7 or the other computer) but if you do as point (3) above I can at least start to help you trouble shoot, and then maybe someone who can really help you might take an interest in your problem.:)