HI there just thought I would share my experience I bought a mastertune and was given a off brand[not mastertunes cable] and had nothing but trouble.I tried for two weeks and even tried a different cable form the local computer store and still no luck.So I called Mastertune and talked to a tech, and he told me my problem was the usb cable and that I should call the folks I bought it from and have them supply me with the mastertune brand cable and it works without any issues at all.I don't know if this will be true for you but it sure solved my problems.The Mastertune usb cable goes Deutsch to RS232 female cable ,to Key,to RS232 male to female cable,RS232 male to usb cable.Worth every penny it works with vista 64 bit and XP