The problem appears to be in the GDL script of Casement_corner 81.gsm
You can try opening it and use Go to Line... (command/control L) in the 3D script. This can be a bit of a crap shoot some times. Since the advent of multiple script windows the line number in error reports is often, shall we say, unhelpful.
You can also search for the DEL statement(s) in the script. If you are unfamiliar with GDL; one of its primary aspects is moving/transforming the coordinate axes with the ADD, ROT, and MUL statements. Each time these are used they add another transformation to the "stack" (they are cumulative in their effect).
The DEL statement removes transformations from the stack. When there are no more to be deleted the DEL will generate this error.
That said, this error should not prevent the part from working properly. If you don't feel like fixing it, you can minimize the annoyance by turning off "Interrupt with Error Messages" in the 3D Imaging preferences (if you haven't already done so).