problem with il command estrudi

[andrea selene]

hi,uso autocad 2011
Despite using polylines or rectangles, the extruded command does not extrude me a solid full but empty as if it only extruded lines.
How can I solve this problem?

 

[GP.]

command: estrudicurrent wireframe density: isolines=4, mode creation of closed profiles
=solid
select objects to extrude or [MOdalità]: moclosed profile creation mode [solido/suhardcore <solido>:</solido>