Mach 3 Stopping part way though a cut. Please Help.

Hi. all. I have a Stepmores Chinese 900x600 CNC router using an early version of Mach3 provided with the machine. It has to date been very reliable. However I now have a problem I can't understand. Doesn't matter what Tap file I run. New or others that have run no problems before...The Machine runs perfectly until Line 500 then Stops with the spindle running down halfway though the job. If I hit the start button the program goes to the end on the screen but the machine does not run. Hitting Run from here also does nothing. Hit reset the program from the start and all is well again until exactly the same place and it stops again.Line 500. Sometimes Line 499. I was having trouble with the old computer running mach 3(The computer would not start) So am using a replacement computer with Mach3 freshly loaded from the disc supplied with the CNC. However I did have this problem just before changing over to the other computer but figured it was just the usual problem I was having with the old one.(used to stop every now and then over the last year or two).This machine uses windows XP and the connection between the computer and Controller is Serial port. Old tech I know but has always worked perfectly. Anyone have any ideas?>???? Getting a bit desperate. Thank you in advance....Regards to all....Ronnie.

500 code lines is the limit for unlicensed Mach3. You need to find the license file (Mach1Lic.dat) on the original CD (or on your old hard drive) and copy it to the Mach3 folder.

500 lines limit is demo.
You will need a licence.

AHHHHA. Thank you. Yes of course. It's been so long (years in fact) since I used the supplied disc and had forgotten to do that. Very much appreciate your help. Stay well and happy...Regards...Ronnie.