how to generate rss feed in asp dotnet c#

Question

i try to generate rss feed using this code ,but it give me a exception at run time as " Cannot attach the file 'c:\users\vikash123\documents\visual studio 2013\Projects\Sample_WebformApplication_RSS\Sample_WebformApplication_RSS\App_Data\aspnet-Sample_WebformApplication_RSS-20150928114944.mdf' as database 'aspnet-Sample_WebformApplication_RSS-20150928114944'."

my code as following

protected void Page_Load(object sender, EventArgs e)

{

string connectionstring = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;

SqlConnection sqlcon = new SqlConnection();

sqlcon.ConnectionString = connectionstring;

SqlCommand cmd = new SqlCommand();

cmd.Connection = sqlcon;

cmd.CommandType = CommandType.Text;

cmd.CommandText = "SELECT TOP 10 * FROM sample";

sqlcon.Open();

rep.DataSource = cmd.ExecuteReader();

rep.DataBind();

sqlcon.Close();

}