I am unable to remove the disc from my Z1 printer.
You must press back and down on the black center hub holder or press down on the rear half of the center hub holder. Do not attempt to lift the CD out of the Z1 without first pushing down on the rear half of the center hub.
If this is still not working, the three tiny springs that push out on the plastic tabs that hold the disc in place may need lubrication. Spray WD40 on a cotton swab and use it to dab oil on the springs.