Interesting, OK.     DO you know where I can download version .042?

If the problem is in fact the card, what is a reputable 4+ axis controller card?   (using 2 axii now but about to add 2 more) hence why I need 4+

The current version on the website is 3.043.062.

Any controller not made in China should work, but I'd ask if it supports G28.1 before purchasing.

What happens if you just run this bit of code no extra bits or edits.

%
G21 G40 G49 G80
G91 G28.1 Y0 Z0
M30
%

Graham - same thing.   This machine gets caught in a loop touching off the Y and Z switches

I downloaded the version of Mach3 from Artsoft's website (v3.043.062) rolling back from the version which came with the machine (v3.043.066) and things still behave the same.

All the code act the same in both versions -ie repeating forever when ran as a gcode file and working as predicted when typed into MDI.

Do you still think this could be the control card?  Is there anything else I can try before trying a different card?

have you tryed to run your M12 Version with

Config -> General Config -> Ignore M calls while loading    enabled?

I just tried "Config -> General Config -> Ignore M calls while loading    enabled?"  and restarted my software and tried again.   Still get the same results, the machine gets to M12 and rewinds to the top of program.. over and over again.

G21                           
G90                           
G53         Z   0               
G0 G54   Y   -79                     
M12                  
G0   Y   -79                     
T1 M6                     S   3250   M3
G43 H1         Z   15               
G1                F   250         

ok tested this here

code M12 macro
DoButton( 24 )
DoButton( 23 )
DoButton( 22 )
DoButton( 25 )

DoOEMButton(133)
DoOEMButton(134)
DoOEMButton(135)

gcode file:
G21                           
G90                           
G53 Z0               
G0 G54 Y-79                     
M12                 
G0 Y-79                     
T1 M6 S3250 M3
G43 H1 Z15               
G1 F250

without any Problem, maybe somebody else can do the test as well, to doublecheck.
   

Thanks for checking!!          What control card you using?       

i tested on my testsystem witch is PP, no motioncontroler.