Error: Object reference not set to an instance of an object.

DataSet ds = new DataSet();
                       conn = new OleDbConnection();
                       conn.ConnectionString = gm.ConnectionString;
                       OleDbDataAdapter da = new OleDbDataAdapter();
                       da.SelectCommand = new OleDbCommand("select * from [ExecutiveMember]", conn);
                       da.Fill(ds);
                       DataRow dtrowdelete = ds.Tables["ExecutiveMember"].Rows[index];
                       
                       dtrowdelete.Delete();
                       ds.Tables["ExecutiveMember"].AcceptChanges();
                       da.Update(ds.Tables["ExecutiveMember"]);
                      MessageBox.Show("Data Deleted!...");