A couple of suggestions:
1. Try starting a new game, instead of loading a saved game and play back your reps then. If they don't crash your game, it's your save games that are corrupt (which can happen if cheats have been used extensively).
2. If starting a new game doesn't help with your existing reps, start a new game and save a new replay to file and play that back. If it works, it sounds like your reps are corrupt and probably useless.
3. Send a rep to someone you know who also has VC (or LC, whatever the replay is) and see if it works on their game. If so, your game has some form of corruption, and will probably need to be re-installed.
You didn't mention if it's simply the playing back of a rep that crashes your game, or the attempted recording of the rep with FRAPS. If it's FRAPS, I'd suggest trying different versions, or updating your vid card drivers.
Outside of that...there's not much else you can do. Hope it works out for ya though.
