BSOD using 16GB, stable with 12Gb

CAD Production Machine
2D and 3D drafting, rendering and point cloud manipulation
AutoCAD, Microstation, Revit, Faro Scene LT, etc.

Windows 7 64 bit
Intel Core 2 Quad Q9550
Asus P5P43TD
Corsair 12Gb (4Gbx3 or 4) CMX8GX3M2A1333C9
Radeon HD 5830 1Gb
500Gb partitioned into 150/350

nothing but problems the last month trying to get my computer to accept the full 16Gb it's supposed to be capable of. i've had to reinstall from scratch 3 times due to system and program errors. logs and dumps are different every time.

i had contacted corsair at some point before the last reinstall and they told me to reset my bios to defaults, which i did and which worked for the most part - on the full 16Gb i had only a couple of random restarts in the week and a half that the system ran, compared to maybe 5 or 6 a day...

the most recent crash, i couldn't even log into windows (got stuck at the login screen) - this was all on 16 gigs of RAM. i reinstalled this past week and it's running great with 12 gig, but i get the BSOD every time i try 16.

i have also contacted Asus wondering why this board claims to be able to run 16Gb. they said because the memory isn't on the board's preferred vendor list.

any help here? is this a hardware or software problem?