Hmm if your using retail all I could suggest is right click on AVP in steam go to properties under the local files tab and click on verify integrity of game cache. It fixes problems for me when i get it freezing and locking up when i try to start a game.
I'm having the same problem. The saved checkpoints keep getting overwritten for some reason. It is infuriating, having fought my way through most fo the marine campaign just to have to start all over again. What rubbish game design is this?
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