为什么打开数据库出现异常后不能关闭窗口？

try
   with DM.ADOQueryMarketer do
   begin
     Close;
     SQL.Clear;
     SQL.Add('SELECT * FROM Marketer Order By Market ASC');
     Open;
     FieldByName('Market').DisplayLabel:='业务员';
     FieldByName('Region').DisplayLabel:='市场分区';
     FieldByName('Tel').DisplayLabel:='电话';
     FieldByName('ShortTel').DisplayLabel:='内线短号';
     FieldByName('Mobile').DisplayLabel:='手机';
     FieldByName('ShortMob').DisplayLabel:='手机短号';
   end;
  except
    begin
    Application.MessageBox('系统出错','提示',0+64);
    Close;
    Exit;
    end;
  end;