Core clocks to high...
Try this in bat for windows
PhoenixMiner.exe -pool eu1.ethermine.org:4444 -wal your adress -worker 5700xt -epsw x -pool2 eu1.ethermine.org:4444 -tstop 70 -tt 50 -cclock 1250 -cvddc 775 -mclock 1800 -hstats 2
pause

I'll update my driver's tonight with those settings and give it a try.