Why would memory cause Driver Problems?

I just picked up a 2X2GB Corsair DDR800 memory kit and installed it next to my 2X1GB kit for a total of 6GB. When I booted the computer, windows could not find my ATI driver. In fact, it said something like "windows could not load this driver (code 46)." When I took out my old sticks it works just fine. When I use the old sticks, it works. I just can't use them together. Anyone know why this is? I'm just going to run the 4GB, its more than enough, but I was still just curious as to why it was causing this problem.

 

It would, because Windows allocates amount of installed system memory for drives. When you went from 2GB to 6GB, tripling the amount of installed system memory, you changed it enough that the allocation pattens (the mental map) no longer match the hardware. Going from 2GB to 4GB was not a large enough change to trigger an IRQ conflict, hence why the new ones work by themselves.

At least that's my guess.