Well, Our software allows for 2 completely separate Machine IDs before another license would be needed. Once the software is installed and the software opened, it asks you to register. The software grabs the computer's machine ID and you also enter an activation PIN. In this instance, the customer installed on a desktop, and then installed in on her netbook. It was working until she did a system restore. Apparently, it changed the machine ID of her netbook. The only thing I can think of is that the system restore somehow altered the machine ID, but I have never seen this happen with a regular HDD.