codice:
$sql = mysql_query("SELECT * FROM users WHERE username='ciao'
AND password='miao' AND activated='1'"); 
    while($row = mysql_fetch_array($sql)){ 
$userid= "$row[userid]"; 
} 
$my_session->my_session_register('userid', $userid);
Prova così:
codice:
$sql = mysql_query("SELECT * FROM users WHERE username='ciao'
 AND password='miao' AND activated='1'");
 
    while($row = mysql_fetch_array($sql)){ 
$userid= "$row['userid']"; 
} 
$my_session->my_session_register('userid', $userid);