c# - ajax combobox not working -

I am trying to use Ajax combobox in my asp.net web forms.

I can use other controls like Ajax Toolkit and I PopupControlExtender etc. But when I use the combo box, it says that the combo box is not a known element.

I right click on the AjaxControl Toolkit in the toolbar -> select the item and confirm that the combo box has been checked but it does not appear in the toolbar

Does anyone know What is the problem or is it facing a similar problem?

Edit :

Code:

  & lt; Div & gt; & Lt; Asp: ScriptManager runat = "server" id = "ScriptManager1" /> Describe how spicy you like your food: & lt; Br / & gt; & Lt; Cc1: combo box ID = "combobox 1" runat = "server" & gt; & Lt; Asp: ListItem text = "lightweight" value = "0" /> & Lt; Asp: ListItem text = "middle" value = "1" /> & Lt; Asp: ListItem text = "Hot" Value = "2" /> & Lt; / CC1: ComboBox & gt; & Lt;% - & lt; ASP: Button ID = "BTN permit" text = "submit" runat = "server" onclic = "BTN SBMTA-click" /> -% & gt; & Lt; / Div & gt; Besides, I've added it after the page directive at the top of my page:  
  & lt;% @ register assembly = "AjaxControlToolkit" Namespace = "AjaxControlToolkit" tagfix = "CC1"%>  
 
 Any thoughts, anybody?