I've been troubleshooting my Xerox 6605DN for hours and cannot find out what is causing this recurring error. I've replaced all 4 of the imaging unit (Black, Cyan, Magenata and Yellow) and still get the same error message "Replace Image Unit." I ended up swapping image units with a machine from another office and found out at that machine, there were no issues. I've tried to reset the Xerox back to manufacture settings from the service menu but was unable to. Please help, I need this machine to keep printing.