List PDF files in a directory with hyperlink to that file in ASP.Net

i googled and got a little code. 

<asp:DataGrid runat="server" id="articleList" Font-Names="Areal"
                    AutoGenerateColumns="False" AlternatingItemStyle-BackColor="#eeeeee" 
                    HeaderStyle-BackColor="Navy" HeaderStyle-ForeColor="White" 
                    HeaderStyle-Font-Size="12pt" HeaderStyle-Font-Bold="True"> 
          <Columns> 
            <asp:HyperLinkColumn DataNavigateUrlField="Name" DataTextField="Name"  
                   HeaderText="File Name" /> 
            <asp:BoundColumn DataField="LastWriteTime" HeaderText="Last Write Time" 
                ItemStyle-HorizontalAlign="Center" DataFormatString="{0:d}" /> 
            <asp:BoundColumn DataField="Length" HeaderText="File Size" 
                ItemStyle-HorizontalAlign="Right"  
                DataFormatString="{0:#,### bytes}" /> 
          </Columns> 
    </asp:DataGrid>

vb

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim dirInfo As New DirectoryInfo(Server.MapPath("policy"))
        articleList.DataSource = dirInfo.GetFiles("*.pdf")
        articleList.DataBind()
    End Sub

the code above lists the files with hyperlink in a afolder but when i click on the link it gives error

The resource cannot be found.

but i ensured that the file is there in folder named policy in my web folder

when i chage the folder name "POLICY"  to " ""(Blank) then it displays the pdf files from my web and the links also works correctly when i change the "" to "policy" then the hyperlink is not working