Printronix ThermaLine Series - Manual (Page 339)

8–7 Error Codes
38 CORNER starting column SC > ending column EC
The left (starting) column parameter of the corner command is greater than
or equal to the right (ending) column parameter.
39 CORNER starting row SR > ending row ER
The upper (starting) row parameter of the corner command is greater than or
equal to the lower (ending) row parameter.