indicates a corrupted fastfat.sys file, or a faulty or incorrect RAM module. The fact that the problem has appeared spontaneously (without any hardware additions), and that you've replaced the file with a known good version leads me to think that a RAM module has failed. You say that you systematically removed the installed RAM - did the stop error repeat when you only had one module installed? Are the modules properly seated in their slots? I'm sure you've checked this, but it's worth mentioning.