^XA
^A0,80
^XZ
....where your program seems to require the font orientation, i.e. "^A0N,80" instead for the second line. But the ZPL manual shows the font orientation will be taken from the previous value (and in fact it seems to default happily to 'N' even if not specified by a prior ^FW command). So your program is unnecessarily strict here compared to the printers themselves.
This would be a good case to show a warning but still assume "^A0," means "^A0N,". Many of our programs here use the first form and it would be great if ZPL Viewer accepted this as valid.