This C6500 prints well with the X3eTY2-10 internal fiery and a catch tray. But as soon as you connect up the optional units namely RU503/504, FD 503 and FS 503, it stops responding to print commands, though makes copies perfectly with these same options. I monitored from the controller job list and noticed that the job actually arrives on the controller but simply disappears without printing after a second or two. Any help will be appreciated.