OK the UC100 is a straight USB controller (nothing to do with the LPT port). You should have pins on the UC100 that you hook the probe to. The UC100 then translates those pins back to Mach3. You would then need to set the pins in Mach3 that MATCH what the UC100 expects for the probe.
IF the UC100 even supports a probe. The info SHOULD be in the UC100 setup manual.
Just a thought, (;-) TP