We have an 8000XL that is randomly giving this error during regular printing.  When I test the stacker in service it all checks out aside from one area.  When I run the Kickers test 1 or 10 cycles at all speeds it works fine but when I run the Kickers and rollers test it will say 'Executing diagnostics....' (see pics) but never does anything, I can't even cancel out of it.  It gets stuck and I have to do a shut down the unit. 
It seems like a logic problem.  HP support had no answer and suggested the main board.  Seems like an easy cop-out answer to me. 
-Terry
 
 
