This is all I could find on info. Seem to be very secretive about details but I cannot blame them. Looks like the software is keyed to a specific Ultracade hardware installation. So you need licensed software as well as your Ultracade number. It is the unique software serial number for the UltraCade computer that there is no real info on. That is why it was guessed that it resides on special hardware that the computer has such as the USBlinx but could also be buried elsewhere.
To quote:
What is an unlock code, GPID or MCID?
Answer: These are serial numbers for parts of your UltraCade system that together create an unlock
code. The unlock codes are required so you can install and play the add-on GamePacks for your
UltraCade system. The MCID is a unique software serial number for your UltraCade computer. You
can view the MCID number by entering the Operator Menu on the UltraCade system. The MCID is
located in the bottom left hand corner of the screen. The GPID is a unique serial number located on
the GamePack CD. Using the MCID and the GPID you can get an unlock code for installation of the
GamePack CD from the UltraCade website (
www.ultracade.com ). The GPID can only be used on
one UltraCade system and cannot be used on multiple systems.