Problems with user defined M1nn codes

Once again I need help. I am attempting to control a parallel port
output pin via the user defined M1nn codes. I have done as instructed
in the EMC V2.3 user manual chapter 12. M Codes. Despite many
attempts to guess the solution EMC2 fails to execute the M code
and issues the “unknown M code error”.

The PROGRAM_PREFIX portion of the file my-mill.ini points to
/home/me/emc2/nc_files

I have placed the external program file M100 in this directory.

I have tried copying the example on page 97 of the user manual
And also tried using M101 code example I found in the examples
Folder.

None of these have worked who knows the correct magic incantation
To make a user defined M code work????

Thanks