textboxwatermarkextender problem

Question

i am using textboxwatermark in my site.

1. firstly i am not getting this tool in my ajax toolbox .
2. if i copy this tool from some other application and paste into my site then it is visible but as soon i set targetid of this tool to the textbox  name then it goes dissapear.

someone pls help me.
thanks in advance.

i have register the ajax assemble. have used script manager.

the code is


 <%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>

 <asp:ScriptManager ID ="SM" runat ="server"  >
 </asp:ScriptManager>

  <asp:TextBox ID ="textbox1" runat ="server" ></asp:TextBox>
 
  <cc1:TextBoxWatermarkExtender  ID="txtPassExtender" runat="server" Enabled="True" WatermarkText="Enter your name" TargetControlID="textbox1"></cc1:TextBoxWatermarkExtender>