error during uploads image file

hallo, when I uploads my images files, I have this error: Errore testata.jpg Impossibile creare la directory wp-content/uploads/2013/05. Verifica che la directory madre sia scrivibile dal server! I checked the root directory, subdirectories and all files, all are readable, writable, and executable. Could you help me? Thank you Elisabetta www.federicoalberati.com