Problema con la pagina principale

Errore Generale
SQL ERROR [ mysql4 ]

Out of memory (Needed 4194260 bytes) [5]

SQL

SELECT COUNT(DISTINCT s.session_ip) as num_guests FROM avphpbb_sessions s WHERE s.session_user_id = 1 AND s.session_time >= 1317666060

BACKTRACE

FILE: includes/db/mysql.php
LINE: 175
CALL: dbal->sql_error()

FILE: includes/functions.php
LINE: 3982
CALL: dbal_mysql->sql_query()

FILE: includes/functions.php
LINE: 4016
CALL: obtain_guest_count()

FILE: includes/functions.php
LINE: 4366
CALL: obtain_users_online()

FILE: index.php
LINE: 131
CALL: page_header()

Salve ho questo problema con la pagina del mio sito mi potete dare una mano?