Problem G-code?

I wrote this parametric G-code program and it seems to run fine on my simulation machine.  But when I try to run it on the real machine it stops at line 20  and gives (Does not exicute line 20) no feedback as to why.  However my simulation machine is running Linuxcnc 2.9, and the real  machine is only on 2.7. 

Line 20 has M0, but normally the next line is the problem, the first G1 move in the routine. Is spindle.0.at-speed true?

And here is a diff, what could be modified from left to right
 

It wasn't spindle at speed, I had checked that first thing. It wasn't the M0 pause, I had tried running it with that line deleted with the same result. Starting the program rhe machine would raise the spindles, start the spindles, move to the starting point, lower the spindles down to 0.25, and pause, At this point clicking the pause button or pressing the next line buttons would have no effect. I tried debugging the parameter that was setting the feed rate before Line 20, and it was what it was supposed to be. I tried deleting the parameter for the feed and expicitly setting the F term with the real feed number, no effect. Deleting the M0 only changed that the pause button on the menu bar wouldn't toggle on, but the machine still would not proceed beyond line 20.

I still don't know what the real problem was, but I restarted the Linuxcnc from the command line to try to see if there were any messages there, and then it ran fine. weird

I'm sorry I don't understand what the point of checking to see if #_task> is equal to 0 in my sub program that is intended to end the program.  And maybe that isn't the best way to do that.  I basically have two branches, the surfacing program can end either at the front or back of the machine depending on where it runs out of space.  Then it needs to raise the spindles, turn them off, and end the program.  Maybe it would have been better to end it like this.