Ok… I think now I understand what is happening…
Yes, I have all the Widget logic done in C++.
However, all the graphic design (layout) is done in the blueprint.
So, then I understood that in order to use StaticClass() the class must be made 100% in C++…
I feel like a fool!! 
Yes, I use C to know that it’s a class made in C++… at least temporarily, because I’m translating my bluprints to C++… it’s just a way to temporarily distinguish it