As always when you leave the house for a few hours 1 slot failed to download. I had removed 'babysitter' from that machine. I rebooted and had the above error which I have never seen. I paused the client and 2 slots (GPU's) out of 3 changed to Core_Outdated. Did a quick duckduckgo search and found a few answers which I did not understand so rebooted yet again. Lost the work unit on one gpu slot but downloaded 2 new work units and off we go again. Can any of you wiz folders explain what happened please in simple terms?