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.
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.