Hi,
The warning refers to the IntegralDefuzzifier you are using to integrate over the fuzzy output, but now that I think about it, you can ignore it. I am actually removing it. What you have to have in mind is that the higher the resolution of the defuzzifier, the more accurate the result will be, but also more computationally expensive. You can set the default resolution of new defuzzifiers with IntegralDefuzzifier::setDefaultResolution(), which will apply to every newly created IntegralDefuzzifier. The resolution of the any given IntegralDefuzzifier can be set with class method [Centroid|BiSector|...]::setResolution().
Cheers.