There is already an open DataReader associated with this Command which
must be closed first

请帮帮我

sqlConnection con = obj.getcon();
con.Open();

       sqlCommand cmd = new sqlCommand("select student_id from student_details",con);
       sqlDataReader dr = cmd.ExecuteReader();
       while (dr.Read())
       {
           String ss=dr[0].ToString();
           if (val == ss)
           {



               sqlCommand cmd1 = new sqlCommand("insert student_vs_testsession_details(student_id,testsession_id,testsession_status) values('" + val + "','" + Test + "','')",con);
               int val1 = cmd1.ExecuteNonQuery();


           }
           else
           {


               string message = "<script language=JavaScript> alert('StudentID does not exists!'); </script>";
               if (!Page.IsStartupScriptRegistered("clientScript"))
               {
                   Page.RegisterStartupScript("clientScript",message);
               }
           }

       } 
     dr.Close();
      // con.Close();

    }