[AChimp]

Either it's a bug in the program working in combination with your system configuration, or it's a bad RAM chip.

This sounds more like a bad RAM chip to me, though, since you can always "read" any address of memory. If you happen to read the wrong one and work with that value, your program will crash or something, but it won't say that the memory couldnt' be accessed.

Does this happen in any other programs?