You must use 15.12 AMD drivers with this miner
It worked flawlessly until now, I think the minimum is 15.12.
i think the deal is its been extensively tested with 15.12. other versions may work though.
i think for rx 4x0 cards you need a much later version to those cards to fire up.
im at 16.something on win7pro x64 with no problems on r9 390.