YOU NEED TO REEMPLACE THE DIMMER, SOMETIMES SWICHTS GET DUST IT AND CORROSIVE SPECIALLY IF ITS OLD.
You want toggle switch that mimics operation of pushbutton, except you want SPDT.
For others finding this thread: Many people want double throw switch for 240V, thinking they have to turn off both hot legs of 240V circuit.
240v can be turned off by cutting power to one hot leg.
My best guess is that something happened with the loads that you are controlling. Did you change light bulbs recently or switch to a different type of lamp - because it sounds like you're having a minimum load issue. The dimmer keeps itself powered up by charging its electronic power supply through the light fixture. But I think it only charges through one of them. So if that one output has too little lighting load on it, the dimmer might not get charged up adequately and give you the issues you're experiencing. The fix would be to increase the lighting load.
That's just a guess, if you want it thoroughly diagnosed, I would contact the manufacturer's tech support center at 1-800-523-9466 - they're available 24/7 and it won't cost you anything.
We're having some confusion on the terminology here which is why I don't think anyone's responded so far.
So, when you say that you want to replace a 2-way wall switch, and replace it with a 3-way programmable timer - I think we're talking about the same type of wiring configuration - so yes, it should work.
The only thing you need to look at is that if this is a 2-way/3-way circuit, then chances are that there is another light switch that controls the same fixture, correct? Some programmable timers do not work with standard, 3-way toggle switches in the other location, you may want to investigate what is required at that spot. I would contact the manufacturer of the timer switch you're using for more information.
There's not a lot of detail in this question, but I'll give it a shot. For the AB-600M-, you do not need a neutral connection at all. In fact, this should wire up like any every-day light switch. What's probably confusing you is that there's probably a blue screw on there. If you're using this in a single-pole application, you don't attach anything to the blue-screw. If you're using this in a 3-way application, the blue screw is used as one of the traveller wires to the other location.
I think that's the best I can do with the information given. My suggestion is for you to call the manufacturer's tech support at 1-800-523-9466 - the're available 24/7 and can help you out a lot faster than an on-line forum every would.
First of all, the ZP260QE is from Lightolier,so you may want to give their tech support center a call.
Secondly, ignore the continuity tests, they tell you nothing. Continuity on the secondary is expected because you're on the output of a "true" transformer, which will look like a short on a DC-supplied continuity test. The input to an ELECTRONIC transformers is a switching power supply, which will not look like anything when supplied by a DC voltage/current during a continuity test. Those test results appear normal to me. The +/- 60 also makes sense, if you've measuring voltages on the output of a dimmer, the impedance of the dimmer's off-state and the impedence of the multi-meter makes for some screwy readings that don't always make sense.
Most dimmers rated for electronic low-voltage have protection circuitry built within them to make sure they're not overloaded. Normal incandescent dimmers will just get warmer than usual, these guys should shut down - perhaps that's what you're seeing.
My two suspiciions are either (a) the additional pendent light, combined with the existing track lights, tripped the overload protection, or (b) when you added the pendent light, you got too much of a current inrush that shorted out the components within the dimmer.