I just attempted to add 2 more gig of memory to my system [running win xp 64bit, fresh install not upgrade] and have come up with some odd errors.
The first error I was getting was when my motherboard was only seeing 3GB instead of all 4GB of memory. After it attempted to boot into windows, I would get a "corrupt or missing windows\system32\config\system error. After finding out how to remap the memory on my motherboard [DFI expert], it was able to see all 4GB.
However, after that little change I now get a "corrupt or missing <win root>system32\ntoskrnl.exe error.
When I take the two new sticks of memory [which are exactly the same as I have in there now], everything works fine.
I've scoured the net without success. Seems quite a few things can cause this error, but the way my situation is, seems a bit different. The threads I have come across that were the same, more or less, had no real definitive solution.
Found my solution. It was simply tinkering with the memory timings.
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Just wanted to add in case someone else runs into this issue. After 3 full days of pure testing, it turns out my motherboard has 2 faulty DIMM slots and my memory [and timings] were fine. I could have saved myself a TON of trouble if I just let memtest run longer than my initial tests.