ajax code error in aspx page

where do i put the code in aspx page if i want to display hover menu,,if i put anywhere in aspx page its throwing errors

the code is

   <ajaxToolkit:HoverMenuExtender ID="hme2" runat="Server"
    TargetControlID="GridView1"
    PopupControlID="PopupMenu"
    HoverCssClass="popupHover"
    PopupPosition="Left"
    OffsetX="0"
    OffsetY="0"
    PopDelay="5开发者_StackOverflow社区0" />

errors like unrecoganized tag filter 'ajaxToolkit' ,,,this name contain upper case character which is not allowed,,like that

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Do you have a ScriptManager on the page with the registered assembly?