Just wished to add that I am also experiencing this constant need to reactivate. It starts when you run the game but get the melee sound effects. Exiting and restarting then brings up the activation screen.
I've just needed to activate for the second time today and the fifth time since I first installed it five days ago.
I have not modified any hardware, software, drivers, ini files, etc.
@botlite, am I to understand that since doing a complete reinstall your issue has cleared up?