Not a guiding issue as I'm not guiding.  Since the absolute encoders didn't log they detected any slew or directed movement, then Ray's theory of slippage of the clutch makes sense.  I'm not sure how the slipping happen.  I feel no slippage when I manually try and move the scope.  The clutch knobs were tightened using a hex key.  Maybe there was some movement elsewhere in the imaging train, but everything seems buttoned down.  I imaged all night last night with no problems, so unless it crops up again, I'm assuming it's just one of those mysteries.

Alex