problems in downloading the file stored in database from gridview column?

See more:

C#

ASP.NET

SQL-Server

File-Upload

i am getting an error "FileNotFoundException was not handled by user code"
[Could not find file 'C:\Users\cgrt\Desktop\MIS\docs\2010-2011']
this is my code :

protected void Button1_Click(object sender, EventArgs e)
    {
        string str = string.Format(@"select m.pcode, m.fyyear, m.date, m.FileName FROM upload AS m where m.pcode = '{0}'", DropDownList1.SelectedItem.Value.ToString());
        SqlDataAdapter da = new SqlDataAdapter(str, con);
        DataTable dt = new DataTable();
        da.Fill(dt);
        GridView1.DataSource = dt;
        GridView1.DataBind();
        DropDownList1.SelectedIndex = 0;

    }
    protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName == "Dwn")
        {
            int index = Convert.ToInt32(e.CommandArgument);
            GridViewRow row = GridView1.Rows[index];
            string fName = row.Cells[1].Text;
            Response.ContentType = "application/octet-stream";
            Response.AddHeader("Content-Disposition", "attachment;filename=" + fName);
            Response.TransmitFile(Server.MapPath("~/docs/" + fName));
            Response.End();
        }

    }

my file is being shown in database table upload and its also stored in docs folder under mis but when i am pressing download button i am getting this error.