Does the false limit trip happen with one axis in home position, or away from home position? I had a similar problem which was caused by the Z axis homing but not moving far enough from the prox switch once homed and causing it to randomly trigger while the other axes were moving. This was also with CSMIO. Fix (thanks to Jazz) was to set Z home position offset 0.5mm from physical home position (Mach3 homing parameters) so trigger clear of switch. Have not had a false trigger since. I had worried that it might be noise problems (limit switch and motor cables in same cable chains, etc) but CSMIO seems pretty good.