assembly surfaces with thickness

[Aeon]

therefore:
I created more or less complex surfaces with the wireframe and surface environment, I went to part design and used the command surface with thickness, getting this:

uploaded with imageshack.usIt's okay.
When I go to assemble I try to contact the surface in orange, with the command "contact" catia prevents me from selecting it, it seems that it does not recognize it as a surface.

How can you solve all this?

 

[Aeon]

I finally managed to find a solution.
instead of using surface with thickness I create an offset of the surface (of the desired thickness), I join it to that of origin and use close surface.
At the end the result is the same but now catia allows me to bind it.
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