Is it getting sufficient power? Are you feeding it with ultra tiny wires or something? Voltage drop could affect it and cause it not to trigger if the wires feeding it are excessively small, but these things only take a few amps, so they aren't big draws. Unless you wired it with cat5 cable or something, I wouldn't really expect it. Make sure you measure the voltage right at the connections on the solenoid when you are activating it. Try it without pressure too.
That is very similar to mine, and it is a massive block of steel. I would find it very hard to believe you could overtighten the 1/4" mounting bolts in any way that could affect it. Perhaps it is possible to overtighten the hydraulic fittings, but I can't see that causing the problem unless you went full gorilla on them.
Could just be a defective unit.