Si Performer 3 FX not working?

OK,m this weekend I wanted to use some reverb on my SI Performer 3, which I think I have done before (certainly on other systems) but I could not get any signal through the FX. I need to know if I'm having a brain drain or the mixer has a fault. I'm assigning inputs to FX1 just as I would for any of the other Mixes, and returning the signal on Layer B on the FX1 fader. No matter what I do it looks like no signal is even getting into the FX system. I can Solo it and get nothing. Our Si Perf3 is pretty much out of the box -- no fancy patching, and we do not use the matrix; just L+R main feeds and a handful of the Mixes. The FX patching is showing LEX-RET1 as the source, which should be correct. Anyone have an answer for this? This should be a very simple operation, and I think I have used the FX before on this console (it was new 2 years ago for us). But I am now officially stumped. Thanks!