Windows XP, stripped. No internet, unnecessary software, power savings or sleep mode enabled.
USB controller
Mach3
Vectric VCarve Desktop software
3D tool paths from .stl file.

Been using this machine and computer combination for 3 years now and a couple months ago a problem started.  The machine just stops executing code.  Might be around line 600 or might be around 6000 but when it happens it will continue to stop at the exact line repeatedly.  If I jump ahead a couple lines and do a "start from here" it will advance may 2 lines and halt.  After clicking on STOP the "Watchdog Trigger" message comes up.  And yes, I have unchecked the config setting and it is always unchecked when it happens. 
Last time (2 projects ago) when this happened I went back and re-created toolpaths and loaded them into Mach.  Ran the complete job without fault.  However I tried the same approach this time and after recreating toolpaths it stopped again in the exact same place. 
Anyone have any experience with this?  Computer?  Mach3 software?  Machine components?  Help!
Kevin C

UPDATE:  So I began to think because the program would stop at the same line of code that the problem is a fixed issue rather than random.  After trying a few possibilities, and after examining the code lines in a text editor, I opened the "edit GCode" in Mach.  Didn't change anything and then saved the file.  After that the entire program ran perfectly.  I'm on the 3rd project (80,000+ lines of code) and no issues.
So I'm wondering if there is a problem with VCarve, when saving the toolpaths is possibly corrupting the gcode.  Anyone ever have such an issue?