Memory could not be "read"

[emond.c]

Ive been having some issues with crashing from a memory could not be "read" error.
An example would be something like
The instruction at "0x76100887" referenced memory at "0x74828d8c". The memory could not be "read".

I have experienced this issue in a couple games, and it appears to happen randomly.

I ran the Windows RAM Diagnostic program, using a boot disk, and ran 2 Extended passes and found no errors.

What might be other probably causes for this error, or could it just be a software problem. FYI, the games ive experienced this in are World of Warcraft and Half-Life 2.

My Specs:

3.0 P4 w/ HT
M955G 800FSB
1.0 GB Kingston DDR400
BFG Nvidia 6800 OC
450W PS
Windows XP Pro SP2

 

[emond.c]

Also it should be noted that I have 5 Fans within the case. The CPU fan, 2 Fans on my videocard, and 2 Casemounted fans.