SQLDataReader - Invalid attempt to read when no data is present

The error occurs when there no data is returned / the data has not been read.

The first case can be checked using HasRows flag

If the data is not read it can be done as follows:

SqlDataReader rdr = Cmd.ExecuteReader();

            while (rdr.Read() == true)
            {
              string sName =  rdr.GetString(1);
            }
      

SQLDataReader - Invalid attempt to read when no data is present