HP Designjet z6 postscript with error 0065-0006-0059.

[TCtech11]

I am working on a HP Designjet z6 postscript 24 inch plotter with error of 0065-0006-0059 during startup.  This error is caused by blockage of the carriage movement due to the starwheel rail being out of position.  With right cover off and door switches tweaked with piece of paper to trigger them, you can watch the printer movements during startup. It starts off in normal operation. The starwheel rail will raise and lower as normal. The carriage will perform its normal operation of traveling back and forth across the printer. Then as the Service station starts up to begin ink prepping and purging. Out of nowhere you can see the rail raise back up and this will block the carriage from moving.  Then the error appears., which is just a paper path error.   We have updated the firmware to the latest Sept date, cleaned the entire encoder strip, reset the printer to factory settings, performed diagnostic checks for all areas of printer which passed in movements and voltage checks.  If you take the rail off completely, the printer functions normally from startup to printing out a job. It advances paper perfectly.  So, what is making the printer bring up the rail out of position at startup... Is this an error in the Main PCA BOARD??   Any thoughts out there- help is greatly welcome!!!!!!!