Hi I've got a Lutron electronic slide dimmer

Let's start whittling away some of the information...

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.