Ivano I got that!
Quick and easy: you don't have to load the entire oxt file into hypenate this!
It normally should work, but for some reason it confuses the plugin.
Just open the .oxt file with winzip, then extract hyph_it_IT.dic file from "dictionaries" subdirectory and load
that into Hypenate this!
This way the hypenation will work.
PS: Sorry for the repeated posting. :P