... but it may not be!|
As the error is an "InternalError 0x50", for "Operator: BeginChar", this perhaps suggests that the printer firmware does not like the format of (or, for some reason, cannot handle) a BeginChar operator (or, more likely, its preceding attribute list).
If you can manage to reproduce the error at will (i.e. it always happens with the same page of a particular document), then repeat the print, but use the 'print to file' option (in the driver Properties dialogue).
Then post the resultant .PRN file here (as an attachment to a reply).
Analysis of the captured print stream should at least confirm whether or not the Operator (and its attendent Attribute list) has a valid format.