An Open Flash Tablet (OFT) can only be used to work with one vehicle at any time. 

After installation, the OFT stores the original ECU memory after a READ process, and keeps it stored to its internal memory. Anytime you work with the OFT to flash a new ROM file to your ECU, it compares the ROM ID (and VIN#) it's "married" with against the chassis' you're working with. 

This is all in an attempt to make reprogramming your vehicle at home as safe as possible, without the possiblity of programming incompatible software.

If you'd like to use your OFT on a new vehicle, you will need to WRITE the original ECU memory back onto the ECU, and then erase the tablet in OFM.