3 way dimmer on 4 way circuit
Looking at the Installation Instructions, if you bought the 3-way version then you either miswired it, or tried to install it in place of one of the 4-way switches previously in the circuit.  The 3-way dimmer must be at one end or the other of the circuit.  (if you bought a single pole aka 2-way, then it'll never work).

This little pic shows the layout.  The solid red bars are for one position of each 4-way; the dashed bars are for the other. So long as this particular 3-way dimmer is in one of the 3-way locations, it always passes the "dimmed" voltage to its live leg.