/// 

/// Downloads (pushes) file to the client browser.  
/// **** NOTE **** Cannot be done from inside an AJAX UpdatePanel control.
/// 

/// The full file path of the file
public void DownloadFile(string fullFilePath)
{
    // Gets the File Name
    string fileName = fullFilePath.Substring(fullFilePath.LastIndexOf('\\') + 1);
    byte[] buffer;

    using (FileStream fileStream = new FileStream(fullFilePath, FileMode.Open))
    {
        int fileSize = (int)fileStream.Length;

        buffer = new byte[fileSize];

        // Read file into buffer
        fileStream.Read(buffer, 0, (int)fileSize);
    }

    Response.Clear();

    Response.Buffer = true;
    Response.BufferOutput = true;
    Response.ContentType = "application/x-download";
    Response.AddHeader("Content-Disposition", "attachment; filename=" + fileName);
    Response.CacheControl = "public";
    // writes buffer to OutputStream
    Response.OutputStream.Write(buffer, 0, buffer.Length);
    Response.End();
}