Got a bit of an interesting problem here... webserver (running Win2k Server) throws STOP errors quite often (Mostly IRQL_NOT_LESS_OR_EQUAL or KMODE_EXCEPTION_NOT_HANDLED). Repair of the O/S did nothing, nor did a clean reinstall. Decided to run Memtest86, and I'm getting large blocks of errors in which the data written to the memory is the inverse of the expected data (IE: expected FFFFEFFF, memory contains 0000100). I suspected the memory, but if the wrong data is being written, I considered the memory controller to be at fault. Any ideas? System Specs: Tyan Thunder S2882 Motherboard 1x Opteron 265 Processor 2GB Kingston HyperX ECC Registered DDR400 RAM (4x512MB). WD Raptor 74GB 10kRPM SATA HDD 650W EPS12v PSU (unsure of brand without opening up the server, but voltages within range) EDIT: Memtest86 also detected something along the lines of 49000 ECC errors. EDIT 2: Ran Memtest without the ECC option on, and it's not reporting any errors (neither the wrong-data errors nor ECC errors).