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I just wanted to give a heads up for people who get this error... Are you mixing RAM? My brother was getting this error all the time until he un-mixed his RAM (which was DDR 400 and DDR 333 until he removed one).
I too get the error semi-frequently (like once every hour or two of gameplay) and am about to remove my "other" RAM stick.
If you get this error, can you verify if you're using two different types of RAM?