Are there any other programs running in the background on your PC ? No other programs running I only use this one to run Mach3 using windows XP.
Are you using X and A selected as a slave ? Yes I have slaved the X and A axis.

I could try swapping the drivers round to see if its sill faulty thing is it's not all the time it will be fine for 5 or 6 times that I use it then it misses a step or more last time it stopped the A axis and it turned the X axis stepper motor quarter a revolution when I hit the stop its going to do some bad damage if I don't get this sorted.