Dear John
I want to thank you so much for the help. I've solved my problem following your instructions.
The matrix S of the cov was singular  because i had few complete observation. I have included 2 wrongs item, because (in the majority of cases) when one is inputed, the other one is "NA", so i have only fews complete observations...
Thank you so much again, for this help and for the great job about SEM( ) that you have wrote and shared on the web.
My best regards,
Costantino Milanese, always the young researcher but with less problems!
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