Problem in join surfaces

Hi everybody,

I have two (theorically) adiancent surfaces realized one with a loft and the other by Extrude/DivisionLine/DeleteFace.

I Said theorically because I see some spaces between theese surfaces but they are realized using the same sketch lines, so I can't understand.

My goal is to join them into a unique solid with a thickness.

Problem:

When I use Join command it seems it works but when I click on the function in the tree it spotlights only a portion, then, when I try to give it a thickness it doesn't works...

anyone can help? I attach the file

thanks