Conversion faild when converting the nvarchar file to data type int.

<asp:TemplateField HeaderText="SaleName" SortExpression="SaleName">
                                <ItemTemplate>
                                    <asp:LinkButton ID="LinkButton1" runat="server"CommandName="Download" CommandArgument='<%# Bind("SaleFileName") %>' Text='<%# Bind("SaleName") %>' ></asp:LinkButton>
                                </ItemTemplate>
                            </asp:TemplateField>

protected void gridContributions_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName == "Download")
        {
      // make sure fileName  contains only file name like 'test.pdf'
            string fileName = Convert.ToString(e.CommandArgument);

            // make sure filePath  contains file path like 'Uploads/Scheme/test.pdf'

             string filePath = e.CommandArgument.ToString();


            string connectionString = WebConfigurationManager.ConnectionStrings["ConnectionString2"].ConnectionString;
            // SqlConnection con = new SqlConnection(connectionString);

            byte[] bytes;
            //string ContentType;

            using (SqlConnection con = new SqlConnection(connectionString))
            {
                using (SqlCommand cmd = new SqlCommand())
                {
                    cmd.CommandText = "select SaleFileName from Sales";
                    cmd.Parameters.AddWithValue("@SaleFileName", SqlDBType.NVarChar );
                    cmd.Connection = con;
                    con.Open();
                    using (SqlDataReader sdr = cmd.ExecuteReader())
                    {
                        sdr.Read(); //Here is throwing an exception saying Conversion faild when converting the nvarchar file to data type int.
                        bytes = (byte[])sdr["SaleFileName"];

                    }
                    con.Close();
                }
            }
            Response.Clear();
            Response.Buffer = true;

            // Read the original file from disk
             FileStream myFileStream = new FileStream( filePath  ,FileMode.Open);
            long FileSize = myFileStream.Length;
            byte[] Buffer = new byte[Convert.ToInt32(FileSize)];
            myFileStream.Read(Buffer, 0, Convert.ToInt32(FileSize));
            myFileStream.Close();




           // // Tell the browse stuff about the file
            Response.AddHeader("Content-Length", bytes.ToString());
            //Response.AddHeader("Content-Disposition", "inline; filename=" & fileName.Replace(" ", "_"));
            Response.AddHeader("Content-Disposition", "attachment; filename=" + fileName + ";");
            Response.TransmitFile(fileName);
            Response.ContentType = "application/octet-stream";

            // Send the data to the browser
            Response.BinaryWrite(Buffer);
            Response.End();
        }
    }