problema con file php

[Clauser]

ecco qua l'errore

Error doing DB query userdata row fetch

DEBUG MODE

SQL Error : 1064 You have an error in your SQL syntax near '' at line 4

SELECT u.*, s.* FROM phpbb_sessions s, phpbb_users u WHERE s.session_id = '' AND u.user_id = s.session_user_id AND session_time >

e le righe incriminate

$sql = "SELECT u.*, s.*
FROM " . SESSIONS_TABLE . " s, " . USERS_TABLE . " u
WHERE s.session_id = '$session_id'
AND u.user_id = s.session_user_id AND session_time > $expiry_time";
if ( !($result = $db->sql_query($sql)) )
{
message_die(CRITICAL_ERROR, 'Error doing DB query userdata row fetch', '', __LINE__, __FILE__, $sql);
}

aiutttoo!!!

[cionci]

Manca la virgola prima di "u" ?!?!?!?