Well, if you are running Norton, then all bets are off. Norton and McAfee both are notorious for causing problems with the game. It may not cause a problem today, but it will eventually cause a problem.
The corruption you found happens as a matter of course for Norton. Norton is the problem.
One of the worst things about Norton and McAfee is you cannot disable them once they are installed. All you can do is turn off the messages. This is due to how they replace system files with their own. Horrible programs.