Method not found: 'Void System.Web.UI.ScriptManager.RegisterStartupScript(System.Web.UI.Page, System.Type, System.String, System.String, Boolean)'.

[MissingMethodException: Method not found: 'Void System.Web.UI.ScriptManager.RegisterStartupScript(System.Web.UI.Page, System.Type, System.String, System.String, Boolean)'.]
   Telerik.Web.UI.RadAjaxControl.PerformRender() +0
   Telerik.Web.UI.RadAjaxControl.OnPageRender(HtmlTextWriter writer, Control page) +1222
   Telerik.Web.UI.RadAjaxControl.RenderPageInAjaxMode(HtmlTextWriter writer, Control page) +33
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +2113547
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +24
   System.Web.UI.Page.Render(HtmlTextWriter writer) +26
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +25
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +121
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +22
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1896

I want to attach a right context menu to a RadGrid .  I followed the instruction in the article:

http://www.telerik.com/demos/aspnet/controls/Examples/Integration/GridAndMenu/DefaultCS.aspx?product=grid

As my data source is a collection, I have to handle the RadGrid1_InsertCommand to insert the new record into database.

But after update database, how can I turn off the grid insert mode? I put

RadGrid1.MasterTableView.IsItemInserted = false; in the RadGrid1_InsertCommand, but I received a exception:

Insert item is available only when grid is in insert mode.

protected void RadGrid1_InsertCommand(object source, GridCommandEventArgs e)

{

GridEditableItem editedItem = e.Item as GridEditableItem;           

      // get sort order

      RadNumericTextBox txtSortOrder =

      editedItem.FindControl("RadNumericTextBox_SortOrder") as RadNumericTextBox;

      int sortOrder = -1;

      Int32.TryParse(txtSortOrder.ValidationText, out sortOrder);

      // InsertIntoDatabase()

      …

      //exception: Insert item is available only when grid is in insert mode.

      RadGrid1.MasterTableView.IsItemInserted = false; 

}

protected void RadGrid1_UpdateCommand(object source, GridCommandEventArgs e)

{

   GridEditableItem editedItem = e.Item as GridEditableItem;

   // get category Id

   Label lblId = editedItem.FindControl("lblId") as Label;           

   int categoryId = 0;

   Int32.TryParse(lblId.Text, out categoryId);

   if (0 == categoryId) return;

   // update database

…

   //works fine

    RadGrid_Categories.EditIndexes.Clear();

}

protected void RadContectMenu1_ItemClick(object sender, Telerik.Web.UI.RadMenuEventArgs e)

{

int iClickedRowIndex;

      bool convertResult = Int32.TryParse(Request.Params["ClickedRowIndex"], out iClickedRowIndex);

      if (!convertResult) return;

      string clickedCommand = e.Item.Text;

       switch (clickedCommand)

       {

                case "Insert":

                    RadGrid1.MasterTableView.IsItemInserted = true;

                    RadGrid_Categories.Rebind();

                    break;

                case "Edit":

                    RadGrid1.Items[iClickedRowIndex].Edit = true;

                    RadGrid_Categories.Rebind();

                    break;

        }

}

protected void RadGrid1_PreRender(object sender, EventArgs e)

{

   GridColumn col = (GridColumn)RadGrid1.MasterTableView.GetColumn("EditCommandColumn");

   if (RadGrid_Categories.EditIndexes.Count > 0 || RadGrid_Categories.MasterTableView.IsItemInserted )

   {

       col.Visible = true;

   }

   else

   {

       col.Visible = false;

   }

}