Just registered to tell you, that you are not alone.

I have the same problem with my Sapphire 280x Dual-x rig with 5 cards.
I dont have a monitor connected and control it with google remote desktop and it seems the problems mostly appears when i connect to it.
Then i have to reboot the machine to get it going again without it halting.
So i guess it has something to do with displaying graphics while hashing.
Dont know if that helps you.

You could try to set the miner to start at boot in windows and dont connect a monitor and see if it works then, by looking at your reported hashrate at the pool.

I have tried everything, like 14.4, 14.6 and 13.12 i have also tried setting virtual memory as high as 300gb :-D
I also tried clocking the cards but it doesnt influence the error, and only gives a VERY small increase in hashrate (like 5-10 more)

Im pretty sure my 280x are also the slow elpida ram, because it only mines with around 400 h/s each.

My 2 other rigs with 3x7950 and 5x7950 have never had the problem, with the same setup.

On another note i hope Claymore can do something about the slow elpida. My old Club 3D 7950 hashes away with 1100/1500 over 500 h/s each.
On stock settings they were 440 each, big increase and hashrate compared to the 280x.