Problem in uploading a file

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ASP.NET

Using this code I'm uploading the file and showing on gridview. But when I click the upload button nothing happen and no error come....

I have checked by debugging when I select the file nothing comes to the object of HttpFileCollection means hfc gives null.

Please help me

protected void btnUpload_Click(object sender, EventArgs e)
{
    HttpFileCollection hfc = Request.Files; // htc gives null
    foreach (string filetagname in hfc)
    {
        HttpPostedFile hpf = Request.Files[filetagname];
        if (hpf.ContentLength > 0)
        {
            int size = hpf.ContentLength;
            string name = hpf.FileName;
            int position = name.LastIndexOf(@"\\");
            name = name.Substring(position + 1);
            string content = hpf.ContentType;
            byte[] filedata = new byte[size];
            hpf.InputStream.Read(filedata, 0, size);
            filedownload.savefile(name, content, size, filedata);

        }
    }

    DataTable dt = filedownload.GetFileList();
    GridView1.DataSource = dt;
    GridView1.DataBind();
}