KOTOR II, there is a level in which you have to complete a set number of tasks to either impress or piss off the local mafia. When you impress them or piss them off enough the game progresses.
But you have to be careful, I wanted to do all the tasks so I jumped between completing them to impress and completing them to aggravate. In doing that though, the game couldn't decide whether I had pissed off or impressed the mafia and so it would not progress.
I only had one save game file so I had to start over. The second time around it happened again (I was just completing tasks as I wanted not paying attention to whether the ending impressed or aggravated the crooks) at least I remembered to save a seprate file before I started the level.
KOTOR II, horribly buggy game.