Samsung SCX-4720FN - Manual (Page 236)

9
T ROUBLESHOOTING 9.31
I encounter error
“Unable to open MFP
port device file!” when
printing a document.
Please avoid changing print job parameters (via SLPR utility,
for example) while a print job is in progress. Known versions
of CUPS server break the print job whenever print options
are changed and then try to restart the job from the
beginning. Since Linux MFP driver locks MFP port while
printing, the abrupt termination of the driver keeps the port
locked and therefore unavailable for subsequent print jobs. If
this situation occurred, please, try to release the MFP port.
Problem Possible Cause and Solution