DataNavigateUrlFormatString for a date

I am trying to pass a date for part of the parameters for the next page. The problem is that the URL string isn't being created in the DataGrid.
Here is the HyperLink field:

 <asp:HyperLinkField DataNavigateUrlFields="CustomerNumber,DueDate" DataNavigateUrlFormatString="detail.aspx?custNo={0}&amp;dueDate={1}"
                    DataTextField="DueDate" HeaderText="Due Date" NavigateUrl="~/Detail.aspx" />
Here the result is:
<a href="Detail.aspx">11/10/2006 12:00:00 AM</a> This should be: <a href="Detail.aspx?custNo=3&dueDate=11/10/2006>11/10/2006</a>
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