Object reference not set to an instance of an object.

Error Caught in Application_Error event
Error in: http://www.kfnl.gov.sa/En/About/ContactUs/Pages/ContactUs.aspx
Error Message:Object reference not set to an instance of an object.
Stack Trace: at Microsoft.Office.Server.WebControls.MetaDataNavTree.OnUnload(EventArgs e)
at System.Web.UI.Control.UnloadRecursive(Boolean dispose)
at System.Web.UI.Control.UnloadRecursive(Boolean dispose)
at System.Web.UI.Control.UnloadRecursive(Boolean dispose)
at System.Web.UI.Control.UnloadRecursive(Boolean dispose)
at System.Web.UI.Control.UnloadRecursive(Boolean dispose)
at System.Web.UI.Control.UnloadRecursive(Boolean dispose)
at System.Web.UI.Page.UnloadRecursive(Boolean dispose)
at System.Web.UI.Page.ProcessRequestCleanup()
at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
at System.Web.UI.Page.ProcessRequest()
at System.Web.UI.Page.ProcessRequest(HttpContext context)
at Microsoft.SharePoint.Publishing.TemplateRedirectionPage.ProcessRequest(HttpContext context)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)