public string eseguiSqlQuery(string nome,string user, string pas,string mail) {
            string ee = null;
            OleDbConnection connection = new OleDbConnection(strAccessConn);
            connection.Open();
            string queryStr = "INSERT INTO utenti(nome,username,password,email) VALUES('" + nome + "','" + user + "','" + pas + "','" + mail + "');";
            OleDbCommand command = new OleDbCommand(queryStr, connection);
            try {
                command.ExecuteNonQuery();
            } catch (System.Data.OleDb.OleDbException oexc) {
                ee = Convert.ToString(oexc);
            } finally {
                connection.Close();
            }
            return ee;
        }   // end eseguiSqlQuery