Here's what the default lathe post produces:

Hello, here's a little problem which is mostly esthetical - except for some Heidenhain controls, it isn't.

Obviously, when there's a subprogram, it's in the middle of everything and thus n$ number is whatever it happens to be at that moment. So when you merge the subprograms at peof$ postblock, you get this:

...

124 L Z+30. F MAX

125 TOOL CALL 0

126 M6

127 L M30

0 LBL 1 ; line number should be 128

1 L IY-21.65 R0 F MAX M99 ; 129 here, and so on

2 L IX-18.75 IY-10.826 R0 F MAX M99

...

So, in Heidenhain control, I'd like to get line (seqment) numbers to just keep counting after L M30.

I think there was some simple way to do this in a post, can't remember it...

(And yes, this is a post problem. I know about "Reset sequence numbers in subprograms" option in Control Definition. If it's not on the line number is just whatever it happens to be at the time the subprogram is created. In this case, 9, 10, 11 etc.)

...and of course, immediately after I posted that, I got rid of the error, by activating "Control supports subprograms" in control definition.

I got the same error. It seems to happen when you use subout$ = 1 at some point. Subprogram system thinks it is making a tooltable with negative tool numbers. An older post (updated from Mastercam 9) doesn't cause this error, so it's a combination of some flag and using subprograms.