Hi Scott,
There is one included example called Subroutine.ngc. Another SubroutineWithConditionals.ngc that shows how to call a subroutine N times - where N may be zero and therefore used as a form of conditional execution.
Problems with your code:
The subroutine must be in the same file and labeled with an O word.
The subroutine should have a return statement M99
It looks as though you have some letter O characters rather than 0 digits.
HTH
Regards
Simple example to call a subroutine 3 times:
Code:G20 G0 X0 Y0 Z0 M98 P100 L3(Call the Subroutine 3 times) M2 (Stop) O100 (Subroutine Label of 100) F40 G1 X1 Y0 G1 X1 Y1 G1 X0 Y1 G1 X0 Y0 M99 (return from subroutine)