"Zero thickness" error in SOL 600 (Patran)

[COLOR=#003366][FONT=Verdana]Hello all,[/FONT][/COLOR]

[COLOR=#003366][FONT=Verdana]I am doing a SOL 600 analysis but Nastran gives me an error of "zero thickness" in some elements. Obviously, I checked those elements and they have properly defined their properties so I don't know what can I do.[/FONT][/COLOR]

[COLOR=#003366][FONT=Verdana]I've done a lot of linear and nonlinear static analysis in that model and all of them have run okey, therefore I suppose that the model is well constituted, where could be the problem?[/FONT][/COLOR]

[COLOR=#003366][FONT=Verdana]The model is all formed by Quad4 elements and Patran version is 2010.[/FONT][/COLOR]

[COLOR=#003366][FONT=Verdana]Thanks in advance. [/FONT][/COLOR]