How do I use the “Mate Search” function of either Houdini 3 Pro x64 or Fritz 12? It doesn’t seem to work… The “Mate Search” function of my two chess engines, Houdini 3 Pro x64 and Fritz 12, does not work.

I click on “Levels” and then on “Mate Search”.



Then a small “Mate Search” window pops up.



When I click on “Parameters” it does nothing. When I click on “OK” the “Mate Search” window just disappears and nothing happens.
In short, you don't have an engine installed that is able to use the mate search function. The scrollable box should show all engines you have installed that are capable of the mate search function, so either you don't have one installed (unlikely if you have a legitimate copy of Fritz 12) or the UI is unable to recognize it for some reason.