hello what control is on your machine. if it is an acramatic a2100 the z position should be 25" (637mm) or thereabouts. z0 is the theoretical position if the spindle nose was touching the table top. please align the machine and check the machine position. ie 2nd icon down on top right of screen then the middle readout at the top will give the machine position, which after aligning should be x0 y0 z25.
if you look in MORE , MACHINE APPLICATION then press tool change along the top you should see the tool change position the carrier needs to be at for tool change to take place.
check the figures and let me know.