4gb (2x2) not working together....

I have a total of 6gb of Patriot memory (2gb-1x2 +4gb-2x2). I have been having glitches in games and already did many HDD test to r/o HDD's. When I'm using the Windows Memory Diagnostics Tool, I seem to have found out that the PDC34G1333ELK memory modules don't want to work properly together. I tested each stick by itself, in each slot, and with and without each of the 1gb sticks. Whenever and wherever (slot-wise) I test the PAIR of 2gb sticks (that came as a 4gb kit together) there is always a "hardware problems were detected...." around 24-30% on the first pass.

Both 2gb sticks will pass the test with one or both of the 1gb sticks. However, in ANY combination that they are together, there is a 'hardware problem'. Is it possible that they don't simply work together? If so, then (out of curiosity) why is that? I am still within my time period to return them to Fry's. I will most likely do it tomorrow. btw the 2gb (1x2) are model PDC32G1333ELK.

And lastly, is there any setting I can do on my mobo that may fix the error? My mobo is an MSI 890GXM-G65, if it helps. I am running Windows Vista Pro. Stock video (for now) with a Happague 1600 TV tuner. my PSU is a CoolerMaster 500w (non-modular). I have one internal DVDRW optical and one 500gb Maxator HDD.

Any help would be awesome!!!!