if (Page.IsValid) {

            OdbcConnection objConn = new OdbcConnection(connectionString);
            objConn.Open();

           string strSQL2 = null;
           string strRole = "Utente";
           string strSQL1 = null;
           int strUserCount = 0;
            
            strSQL1 = "SELECT Count(*) FROM Users WHERE username='" + txtUsername.Text + "'";

            OdbcCommand checkUsername = new OdbcCommand(strSQL1, objConn);
      // ERRORE QUI!
        strUserCount = checkUsername.ExecuteScalar();

                if (strUserCount == 0)
                {
                    strSQL2 = "INSERT INTO Users (Fullname, Email, Username,Password,role,Info)";
                    strSQL2 = strSQL2 + " VALUES ";
                    strSQL2 = strSQL2 + "('" + txtFullname.Text + "', '" + txtEmail.Text + "', '" + txtUsername.Text + "', '" + txtPassword.Text + "','" + strRole + "','" + txtInfo.Text + "')";

            
                    OdbcCommand addUser = new OdbcCommand(strSQL2, objConn);
                    addUser.ExecuteNonQuery();
                    objConn.Close();
                    Response.Redirect("login.aspx");
   
                }
                else
                {
                }

                objConn.Close();

        }