Following this thread since i got the same problem after updating Windows. For while I could only get 4/6 gpus working (code12) on the others but trying all possible fixes got me to 5/6. Now done wasting time finding a solution, 6/6 cards worked before win update....
Hopefully someone solves this, I maxed out my technical potential on this one...
How'd u get 5 working?
Well first of all as I said I had just 4/6 and couldnt do anything. So I cleaned drivers and started by plugging them in one by one, thinking there was a problem with me installing windows with all cards hooked up. Then I got stuck on the third card. 2 working, 1 with code 12. So I did all the fixes, regedit hackflags, updating bios to ver1.30 enabling 4G-decoding option, turned off onbard audio etc. Changed swapfile to 16gb-32gb.
When nothing of that worked I figured after reading this thread and it seems to be an problem with windows 10 ver. 1079, okay I'll plug in all six and just mine with however many cards I can. But then 5 cards run problemfree, and code 12 error on just 1. So thats what I did, cant explain it any better, sorry. Mining at the moment with 5 and only hope of getting 6 working is this thread it seems...