As Skuzzy said, anti-xxx (-virus, -malware, -unwanted) program can break the functionality of AH - or any other program. It doesn't matter if you haven't done anything to any file system or your computer, they may likely have done something after an automatic update which they do on a daily basis or even more often. Not to forget Windows updates which also happen automatically in the background. They certainly do things to system files! And Lunatic, you certainly must have updated the game during the last three months in order to be able to play. Updating changes files and as the above proves, there's many variables involved in that changing.
Another thing that may be far fetched is using an SSD for AH. I understand that they update files in a different way compared to HDD's which is why updating AH on an SSD can cause issues. Does the same apply to the in-game micro updates, I don't know? Anyhow, issues after a few hours playing might fit into that category. Just guessing here.
