Now the user opened properties, and under "open with.." selected my App, after doing this everything works fine. This could be enough for now, anyways i still have doubts, maybe this will always happen when my app is installed on Win7 or maybe this user just tempered my App's file Extension or something, if this is the case then there is nothing to worry about. I'll keep this thread unresolved for a while until I (or anybody) can test Aaron's code in a computer with Win7 and see what happen, thanks to everybody, reps to everybody too.