When I get an M3, Mach3 stops processing my g-code.  If I take out the M3 everything seems to work.

I noticed I get a couple of notify messages, notably 3 and 5, and I do nothing when I receive them.

I assume I must give some kind of response to "engine" to tell it to start reading the g-code again, but I don't know what to do.

Any help?