You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near 'creation_date VALUES '1089387219' where uid=29d7095aa61752f903f
Codice PHP:
$tempo= time();
$queryb = "INSERT INTO ".$_CONFIG['table_sessioni']." creation_date VALUES '$tempo' where uid=".$uid." ";
$result = mysql_query($queryb) or die(mysql_error());