Hi Rolige,
thanks for your answer. You had right! It was a module issue. Reading your answer, it had noticed that when I was logged in the cart ajax request returned 302.
Searching on web, I found that the issue was the token inside the button-cart.tpl. I had modified the static string with {$static_token} and so now it's working.
I hope that this is useful for anyone.
Stek
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