I had this happen twice to me... once it was a bad connection to one of the Gridseeds, after resetting all the cables it fixed it... the other time it ended up being a gridseed that went bad, took me awhile to find out which one was throwing all the hardware errors (which is why I wish they showed HW errors per each device in addition to the submitted/accepted).. once I replaced it I've been fine. I'm running 12 off a single powered usb hub @ 850. I also have mine restart the miner every 6 hours. Been rock solid stable the last few days... which is good since I'm going to be gone the next 3 days and I hope they keep going no problems during that time.