Image Control NavigateURL Property

Hi,
VS2005 + VB

Why is it the NavigateURL property of my image control (<asp:image>) doesn't work when I code like something below. When I point my mouse to the image displayed, the cursor doesn't change to hand shape. 
<asp:Image ID="imgCellection" runat="server"
ImageUrl='<%# FormatURL(DataBinder.Eval(Container.DataItem, "InvNo")) %>'
NavigateUrl='<%# "~/ColDtl.aspx?InvNo=" + DataBinder.Eval(Container.DataItem,"InvNo") %>' />
Thanks for help,
Garreth
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