An interesting anomoly I discovered in subroutines is that there has to be a return at the end of the M99 line of Mach is unhappy. This behavior was with imbedded subs, but may also be true for extrenal subs.
There is a recent version of Mach that would skip the next line of code in the main program after returning from a sub, so watch out for that . . . I think it may have been .26 but the Changelog has the info.