C# - LinkButton Not Doing Postback On Second Click?

I want the clients to be able to download a PDF file. So I've put on a LinkButton with the code:

Markup:

<asp:LinkButton ID="lnkPrintHere" runat="server" OnClick="lnkPrintHere_Click" Text="Click here" />

Code behind:

protected void lnkPrintHere_Click(object sender, EventArgs e)
{
Response.ContentType = "application/pdf";
Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName);
Response.TransmitFile("/_layouts/Files/" + fileName);
Response.End();
}

Everything works fine the first time the link is clicked. Subsequent clicks don't raise the OnClick event.