ขอวิธีแก้ไข htmlfile access is denied หลังจากสั่ง FileUpload Click ใน javascript ครับ

function fupPDFclick() {
       document.getElementById('<%= fupPDF.ClientID %>').click();
}
function fupPDFchange(obj) {
       document.getElementById('<%= txtFileUploadPDF.ClientID %>').value = Filename(obj.value);
}

<asp:TextBox ID="txtFileUploadPDF" runat="server" SkinID="ReadOnlyBox2"></asp:TextBox>
<asp:ImageButton ID="btnUploadPDF" runat="server" ImageUrl="~/Images/Upload18.png" OnClientClick="fupPDFclick()" />
<div style="display: none">
     <asp:FileUpload ID="fupPDF" runat="server" onchange="fupPDFchange(this)" />
</div>