Cannot unregister UpdatePanel in Radgrid

[RB]

I am creating a RadGrid as follows:

protected override void OnInit(EventArgs e)
      {
          this.Controls.Clear();
          this._RadLoadingPanel.ID = "_RadLoadingPanel";
          this._RadLoadingPanel.Transparency = 30;
          this._RadLoadingPanel.Skin = "WebBlue";
          this._RadLoadingPanel.BackgroundPosition = AjaxLoadingPanelBackgroundPosition.Center;
          this.Controls.Add(this._RadLoadingPanel);

          this._RadGrid1.Skin = "WebBlue";
          this._RadGrid1.Width = Unit.Percentage(98);
          this._RadGrid1.GridLines = GridLines.None;

          this._RadGrid1.AutoGenerateColumns = false;
          this._RadGrid1.AllowSorting = true;
          this._RadGrid1.GridLines = GridLines.None;
          this._RadGrid1.PageSize = 100;
          this._RadGrid1.PagerStyle.Mode = GridPagerMode.NextPrevAndNumeric;
          this._RadGrid1.ShowGroupPanel = true;
          this._RadGrid1.AllowPaging = true;
          this._RadGrid1.AllowSorting = true;
          this._RadGrid1.EnableLinqExpressions = false;
          this._RadGrid1.MasterTableView.NoMasterRecordsText = string.Format("There are no documents associated with this order / quote / proposal.");
          this._RadGrid1.MasterTableView.Width = Unit.Percentage(100);

          this._RadGrid1.NeedDataSource += RadGrid1_NeedDataSource;

         // Setup Columns
          GridBoundColumn boundColumn = new GridBoundColumn();
          this._RadGrid1.MasterTableView.Columns.Add(boundColumn);
          boundColumn.DataField = this._DocList.DescriptionColumn.ColumnName;
          boundColumn.HeaderText = "Document Type";
          boundColumn.UniqueName = "DocumentType";
          boundColumn.AllowSorting = true;

          this._UpdatePanel.Unload += new EventHandler(UpdatePanel_Unload);
          this._UpdatePanel.ID = "ajaxPanel";
          this._UpdatePanel.UpdateMode = UpdatePanelUpdateMode.Always;
          this._UpdatePanel.ContentTemplateContainer.Controls.Add(this._RadGrid1);

          this.Controls.Add(this._UpdatePanel);

          base.OnInit(e);

      }
protected override void OnPreRender(EventArgs e)
      {
          _RadGrid1.MasterTableView.Rebind();
          base.OnPreRender(e);
          var ajaxManager = RadAjaxManager.GetCurrent(Page);

          if (ajaxManager != null)
              ajaxManager.AjaxSettings.AddAjaxSetting(this._UpdatePanel, this._RadGrid1, this._RadLoadingPanel);
      }

It gives the following error:
Cannot unregister UpdatePanel with ID 'ajaxPanel' since it was not registered with the ScriptManager. This might occur if the UpdatePanel was removed from the control tree and later added again, which is not supported.
Parameter name: updatePanel

After reading in forums I added the following:

void UpdatePanel_Unload(object sender, EventArgs e)
     {
         MethodInfo methodInfo = typeof(ScriptManager).GetMethods(BindingFlags.NonPublic | BindingFlags.Instance)
     .Where(i => i.Name.Equals("System.Web.UI.IScriptManagerInternal.RegisterUpdatePanel")).First();
         methodInfo.Invoke(ScriptManager.GetCurrent(Page),
             new object[] { sender as UpdatePanel });
     }

This did not resolve it. I even added this.COntrols.clear, but did not work. When I comment out the  boundColumn.DataField = this._DocList.DescriptionColumn.ColumnName; statement, it displays a grid.
Please help me resolve this.

[RB]

I forgot to mention that this Radgrid is placed inside another Update Panel.

[Eyup]

Hello Ruchi,

Please note that using UpdatePanel simultaneously with RadAjaxManager or RadAjaxPanel( or implementing multiple wrapped UpdatePanel) is not a supported scenario and we highly recommend to avoid such implementation. Please either use just the manager to update your controls replacing the UpdatePanel / RadAjaxPanel with a regular asp:Panel, or use the UpdatePanel / RadAjaxPanel alone to wrap your page:
http://www.telerik.com/help/aspnet-ajax/ajax-controls-in-ajaxpanel-and-ajaxsettings.html

In addition, when creating a RadGrid control programmatically, you should strictly follow the steps provided in this article:
http://www.telerik.com/help/aspnet-ajax/grid-programmatic-creation.html#Section22

And finally, remove the Controls.Clear() and instead of adding the controls directly to Page.Controls using this.Controls, use an asp:PlaceHolder or Form.Controls.Add.

Hope this helps.

Regards,
Eyup
Telerik