Intergrex 500 Problem

[Htech]

INTERGREX E500HS/640M PRO:

I am having a problem with the Z-axis, I cannot hold a depth of + or – 4thousands, when I insert my Z-axis offset to compensate, the Z-axis will float again. MAZAK has been out here and looked at the machine and found no problems. Our programmers know the program is correct for the fact we can run the same program on a different machine. Has anyone encountered this problem, if so, please tell me.
The machine is 1 year old and there is no backlash in the ball screw.