HP PCL 5 Reference Manual page 362

ERROR=NONE
If the entity type and location are valid, but there are no entities of the
specified type in that location, or if the type is inappropriate for the
specified entity (internal user-defined pattern or currently selected
macro), then an error response is generated. For example, if you
request the downloaded symbol sets and there are no downloaded
symbol sets, the following error response would be generated:
ERROR=INTERNAL ERROR
The status response for some requests can be fairly large (such as
for fonts). In processing status responses, if the printer runs out of
memory, an internal error is returned, as shown below:
Note
The error conditions described above are the only conditions for
which an error response is generated. If you make a syntax error in
the escape sequence, or send a command which the printer cannot
interpret, the printer ignores the command and no error response is
given.
16-20 Status Readback
PCL
INFO SYMBOLSETS
ERROR=NONE
PCL
INFO SYMBOLSETS
ERROR=INTERNAL ERROR
EN