view image from database to asp page

Hi,
I am try to view an image from database. I used handler and invoke it by following code..

<asp:GridView ID="gvImage" runat="server" AutoGenerateColumns="false">
<columns>
<asp:TemplateField >
<ItemTemplate>
<asp:Image ID="Image2" runat="server" ImageUrl='<%# "ShowImage.ashx?StudentID=" + Eval("StudentID") %>' AlternateText="N/A" />
</ItemTemplate>
</asp:TemplateField>
</columns>
</asp:GridView>

But it not working. The error flashes is.....
Conversion from string "ShowImage.ashx?StudentID=" to type 'Double' is not valid.

[Resolved]