Techdemo keeps crashing

I run the techdemo on 3 different computers. My main desktop I use the techdemo on keeps crashing when I go exit the game. What causes this? Also if I buy the full verison can it be installed on more then one computer? Or do I have to pay for each computer?

 

I think it can be used on two computers on the same network. (Not sure about the two part but I know the computers have to be on the same network so the key doesn't get banned)

 

So if somebody's parents split up and he bought the game, they would have to buy it twice??? That's dumb...