There is already an open datareader associated with this command which must be closed first

using (SqlCommand readCompu = new SqlCommand("select [computer name] from computer", con))
            {
                SqlDataReader readComputers = readCompu.ExecuteReader();
                while (readComputers.Read())
                {
                    
                    commppName = readComputers[0].ToString();
                    if (listAllConnectedComputers.Items.Contains(commppName))
                    {
                        //Update Computer set status='Connected'
                        using (SqlCommand insertToDB = new SqlCommand("update computer set [Computer Status]='Connected' where [computer name]='" + commppName + "' ", con))
                        {
                            insertToDB.ExecuteNonQuery();
                        }
                    }
                    else
                    {
                        //Update Computer set status='Disconnected'
                        using (SqlCommand inseritToDB = new SqlCommand("update computer set [Computer Status]='Disconnected' where [computer name]='" + commppName + "' ", con))
                        {
                            inseritToDB.ExecuteNonQuery();
                        }
                    }
                } readComputers.Close();
            }