In order to use message files in a program, the message source files (with .msg extension) must be compiled with the fglmkmsg utility to produce compiled message files (with .iem extension).
fglmkmsg mess01.msg
This creates the compiled message file mess01.iem.
fglmkmsg mess01.msg mess01.iem
The .iem compiled version of the message file must be distributed on the machine where the programs are executed.