Thank you for the replies gents, to add to the mystery, this morning E-link decided to work; must have been because the sun was out. Worked ok to run a loco so popped the new class 37 on, switched to program terminals - would read not the CV. Put a previously programmed loco on, read CV ok Put new train back on, could read and edit CV1 and 29, but failed to read back and confirm. Tried another decoder (both were Bachmann 36-568A) same issue but initial reading is intermittent, sometimes it works. The decoder that I successfully changed CV1 and 29 on would not run the train. I suspect the actual loco circuit board is faulty, runs fine on DC. I have a choice of 2 issues: Faulty loco and intermittent E-link.Faulty loco which temporarily screwed up the E-link so much that several reboots yesterday would not fix it. Time to call the shop... Hey 96RAF, I see you were a Halton guy - Rigger or Sooty? I was Cosford trained - Air Radar back in 1979... Probably not allowed to call air electronic trades 'Fairies' these days for fear of being shut down...