Engen Petroleum Ltd. - Error

System.NullReferenceException: Object reference not set to an instance of an object.
   at MaterialList.Page_Load(Object sender, EventArgs e) in e:\WebSrv\Inet - www.engen.co.za\wwwroot\home\apps\msds\MaterialList.aspx.cs:line 21
   at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e)
   at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
   at System.Web.UI.Control.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)