It helps if you describe what "it wont work at all" means.

Does it show your messagebox?
Is an error generated?
Does the program just crash?

You are saying you are having problems on 64bit machines. Was it developed on a 64bit or 32bit machine?

Removing the On Error Resume next may give you an idea what the problem is. I'm guessing if you were to check what is being returned in steamexe you will find it isn't what you expect.