Object reference not set to an instance of an object.

at CommonMenuEntityHelper.GetCommonMenu(Int32 menuId) in c:\webspace\bacs.vn\httpdocs\App_Code\NTTHAO\Sites\CommonSite\CommonMenuEntityHelper.cs:line 24 at NTTHAO.CommonWeb.CommonUserControl.GetRootMenu() in c:\webspace\bacs.vn\httpdocs\App_Code\NTTHAO\CommonWeb\CommonUserControl.cs:line 272 at Sites_Template_Webparts_Pages_Default.Page_Load(Object sender, EventArgs e) in c:\webspace\bacs.vn\httpdocs\Sites\BAC\Webparts\Pages\Default.ascx.cs:line 38