In general, the output of a solid state relay could be:
(1) a triac (or bi-thyristor) for AC load.
(2) a MOSFET or bipolar transistor for DC load.
Usually a triac, thyristor or bipolar transistor could be turned on by a current supplied to the gate or base (in case of MOSFET, by a voltage).
In optoisolator ICs (may be called optocoupler), the input current produces an internal light beam that, in turn, stimulates the internal opto gate or base.
Yes true, But what is causing the Solid states relays output to BLOW a SHORT or OPEN on it's output? it will Blow the Triac or Mosfet, what causes this to happen? OVER LOADING IT and what else?
I see now. You meant faulty optoisolator ICs having an output shorted or opened always even if they are driven properly.
I am afraid that your question is general. So I can say the causes, for these faults to happen, are much like the ones that damage conventional triacs, Mosfets and transitors (not opto).
By specifying a circuit (also the main components it uses) and how it is supposed to work, it would be possible seeing the possible cause or causes for its failure.