If you get errors while using this tool, please update .NET Framework and check if you accidentally deleted the .dll file that comes with the download. If you have, just download it again and don’t delete anything.
Also, if you're not lucky and the account you want to hack is protected with a very long and strong password, then you might want to consider using a keylogger or a phisher to obtain access to that account. But, this really is extremely rare and you should be just fine by using only FPS.