MaskedEditValidator doesn't work in EditItemTemplate of gridview

Hellp,

i want to use the ajaxToolkit:MaskedEditValidator for checking a textbox, but i get the error: Object reference not set to an instance of an object.

I guess it is due to the fact the ajaxtoolkit is within a template and is unable to find the targetcontrolID.

Thanks

<asp:GridView ID="GridView1" runat="server" ...

<asp:TemplateField HeaderText="az">
<EditItemTemplate><asp:textbox ID="dt" runat="server" ... ></asp:textbox>
<ajaxToolkit:MaskedEditValidator ID="MaskedEditValidator1" runat="server"
TargetControlID="dt"
Mask="99/99/99"
MaskType="Date">
</ajaxToolkit:MaskedEditValidator>
</EditItemTemplate>
</asp:TemplateField>

</asp:Gridview>