mysql_fetch_object(): supplied argument is not a valid MySQL result resource

[fanrpg]

schon wieder ein Problem und ich weiss nicht warum <_<

PHP-Code:

<?php
$catsql = "SELECT * FROM `cat` ORDER BY `ID` DESC";
$catquery = mysql_query($catsql);
while($catrow = mysql_fetch_object($catquery))
{
$catname = $catrow->name;
$catdesc = $catrow->desc;
$caturl = $_GET['download'] == "$catname";
$caturl = str_replace(" ", "_", $caturl);
echo "<table border=\"0\"><br>
<tr>
<td><a href=\"$caturl/\">$catname</a><br>
$catdesc</td>
</tr>
</table>";
}
?>

was stimmt daran nicht?
Der gibt mir nämlich folgendes aus:

Warning: mysql_fetch_object(): supplied argument is not a valid MySQL result resource in on Line 4

...

Was zur Hölle ist falsch?