Warning mysql_fetch_array supplied argument is not a valid

Jeg får følgende fejl:

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource on line 13



Warning: mysql_free_result(): supplied argument is not a valid MySQL result resource on line 24

Min kode er:

<?php

$result1 = mysql_query("
SELECT overskrift.tekst, indhold.indhold
FROM overskrift INNER JOIN
    side ON overskrift.id = side.fk_overskrift_id INNER JOIN
    indhold ON side.fk_indhold_id = indhold.id
WHERE side.id ='".$_GET['id']."'");

$row1 = mysql_fetch_array($result1, MYSQL_ASSOC); {
?>

<?php echo $row1['overskrift']; ?><br><br>
<?php echo $row1['indhold']; ?>
   


<?php
}

mysql_free_result($result1);

?>

Hvad er fejlen?