Hey guys,
I have a problem with the machine making a radius when it should be a hard 90 deg. turn.  It seems to only be when the machine goes from +X to -Y. 
I have played around with the velocity settings and it seems that the error gets greater as the velocity increases.
I have used the same program block by block and it works fine.
Any suggestions??

In General Config, check "Stop CV on angles >" and set it to 89°.

Your in CV move, and Mach3 is trying to maintain a constant velocity as it goes around the corner.