There is a horrible bug on the PC version which may lead to people reloading checkpoints, but is rather easy prevent... if not time consuming and a complete crock of shit that it happens. When you do the bit where you re-enable 4 computer firewalls, you are supposed to return to joe security and complete the quest, well me and my buddy found we had no waypoint whatsoever... I noticed that his animation was stuck, he was right next to three chairs.... so naturally I started swinging at him and when one of the chairs moved, so did he! Only a bit though... My friend and I continued to kick the cushioney shit out of said chairs until they were completely out of the way. He started walking again, went to the desk and next waypoint of mission unlock.

Just a heads up as it has apparently been happening to a few people.

I didn't have issues with that mission myself, but I did notice him getting caught on those chairs slightly. At first I thought he was trying to sit down on an overturned chair.

Yeah, this also happened to me on 360, but it was because i moved the chairs when I was looting all the computers underneath that desk for batteries and such.