screening impedance hfss

Hi

I am new with the HFSS software. I just need to simulate a periodic structure of square-lopps, and I am having a lot of troubles. I already know how to design the unit cell:
draw my square loop,I put a air box around which same size (x and y axis) but really big(z axi), i put the two perfect E and two perfect H boundaries conditions in the faces of this airbox, 2 wave ports, set up solutions

now I make another design,I draw airbox, put the two perfect e and two perfect H in the faces,2 wave ports, set up solutions, draw a rectangle in the middle of this airbox,and, here comes my problem, assign an screening impedance boundarie to this rectangle, because my structure works with hundreds of square-loops togethers. when I simulate I get diferent errors. I dont know if I should use fast sweep or interpolating sweep, I have tried both without result..

when I use fast sweep the error says " fast sweep cant be use because of problems with screening impedance boundaries..

when I use interpolating sweep the error says "interpolating sweep did not converge"

another times I get "invalid screening impedance from linked data"
I really dont know what to do..

I will leave the hfss file if anyone want to see it

I will really appreciate whatever help.

Thanks very much