Sql server connection is open but can't fetch data

string connetionString = null;
SqlConnection cnn;
connetionString = "Data Source=.\\SQLEXPRESS;Initial Catalog=master ;Integrated Security=True";
cnn = new SqlConnection(connetionString);
try
{
   cnn.Open();
   SqlCommand thisCommand = cnn.CreateCommand(); 
   thisCommand.CommandText = "select  * from spt_fallback_dev";
   SqlDataReader thisReader = thisCommand.ExecuteReader();
 
   if ( thisReader.Read())
   {
      MessageBox.Show("its damn reading ");
   } 
   thisReader.Close();
   cnn.Close();
 
   MessageBox.Show("Connection Open ! ");
...