I'm having "GPU returned incorrect data!" on my mixed 290/280 rig. Despite errors galore the rig gives only about 1% of rejected shares on the pool side even though the log is all red at times. None of the cards is overclocked, they are undervolted however with AB. What might be the cause of it?

http://image.prntscr.com/image/c8ae8a63174747b7960cd0d0bfb86885.jpg