If your i1iO table is failing to calibrate, please try the following steps.
First, remove the i1Pro from the i1iO and try running i1Diagnostics 2.5.1 on it alone to verify that your table is functioning correctly.
Please be aware that the teflon glide ring that sits beneath the i1 instrument has two metal wire clips that must be underneath two plastic ears, to ensure that the instrument is able to lock down into the correct position. If the wire clips are above the plastic ears, please carefully move the wires beneath them, being careful to not snap them off.
Next, when you reseat the i1Pro in the i1iO holder, press on the top of the instrument gently with the heel of your hand to make sure that the i1Pro is fully locked into the holder. If you are looking at the i1Pro from above as it calibrates or measures, you should not see any light leaking out from the i1Pro's optics. If you see this light, stop your measurement and re-seat the i1Pro.
Assuming that your i1Pro is working as it should, be sure that the calibration plaque is flush against the surface of the table. If the plaque is raised, there is a possibility that it will not remain completely level, which disrupts the calibration process. If you need to make a head height adjustment for your substrate, do your calibration first, then adjust the head height at the step where the software asks you to mark your testchart coordinates.
After you have established that the i1 instrument is correctly seated in the clear plastic holder tray, here's a procedure that will establish correct height for the i1.
By turning the adjustment knob at the top of the arm, take the i1 up to the top of the adjustment range (raising the i1), until you experience slight resistance. Now turn the knob in the other direction to take the i1 down to the table's surface, again stopping when you experience resistance. Now back the knob off between 1/8th to 1/4 turn. We've found that this level should be appropriate for most targets printed on papers.