Meaning: Failed to process the plate knuckles on an imported plate. The plate surface is not marked for knuckles. This happens for imported surfaces created from a SAT file with no attributes or bad attributes for the knuckle edges.
Correct the imported plate's SAT file with the appropriate attributes for the knuckle edges.
Perform an update/recompute.
If the problem persists, report steps taken and include the SAT file to your support group.