Fejl i php side

Nogen der kan hjælpe mig med denne lille fejl?

Fejlen:

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /customers/nixx.dk/nixx.dk/httpd.www/includes/classes.php on line 39

Siden:

<?
require "header.php";
require "subheader.php";

require "navigation.php";
require "sidebar.php";
echo "</td>
<td width=\"10\"></td>
<td valign=\"top\">\n";
tablebreak();
if (empty($cat_id)) {
    opentable("Knallerter");
    $result = dbquery("SELECT * FROM ".$x2_prefix."Knallert_cats ORDER BY Knallert_cat_name");
    $rows = dbrows($result);
    if ($rows != 0) {
        $columns = 2;
        $counter = 0;
        $tab = "<table width=\"100%\" cellspacing=\"0\" cellpadding=\"0\" class=\"body\">
<tr>\n";
        while($data = dbarray($result)) {
            $result2 = dbquery("SELECT count(Knallert_cat) FROM ".$x2_prefix."Knallerter WHERE Knallert_cat='$data[Knallert_cat_id]'");
            $num = dbresult($result2, 0);
            if($counter % $columns == 0) {
                $tab .= "</tr>
<tr>\n";
            }
            $tab .= "<td align=\"center\" valign=\"top\" width=\"40%\"><a href=\"$PHP_SELF?cat_id=$data[Knallert_cat_id]\">$data[Knallert_cat_name]</a> <span class=\"small2\">($num)</span>";
            if ($data[Knallert_cat_description] != "") {
                $tab .= "<br>
<span class=\"small\">".stripslashes($data[Knallert_cat_description])."</span>";
            }
            $tab .= "</td>\n";
            $counter = $counter + 1;
        }
        $tab .= "</tr>
</table>\n";
        echo $tab;
    } else {
        echo "<br><div align=\"center\"><h3><b><u>Siden er, under opbygning!</u></b></h3>
        Hvis du har et svar på fejlen, så kontakt Admin!</div><br>
        <table width=\"100%\" cellspacing=\"0\" cellpadding=\"0\" class=\"body\">
<tr>
<td align=\"center\">Ingen Knallert kategorier, blev fundet</td>
</tr>
</table>\n";
    }
    closetable();
} else {
    $result = dbquery("SELECT * FROM ".$x2_prefix."Knallert_cats WHERE Knallert_cat_id='$cat_id'");
    $data = dbarray($result);
    $cat_name = stripslashes($data[Knallert_cat_name]);
    opentable("Knallerter: $cat_name");
    $itemsperpage = 15;
    $result = dbquery("SELECT * FROM ".$x2_prefix."Knallerter WHERE Knallert_cat='$cat_id'");
    $rows = dbrows($result);
    if (!$rowstart) {
        $rowstart = 0;
    }
    if ($rows != 0) {
        $totalpages = ceil($rows / $itemsperpage);   
        $currentpage = $rowstart / $itemsperpage + 1;
        $result = dbquery("SELECT * FROM ".$x2_prefix."Knallerter WHERE Knallert_cat='$cat_id' ORDER BY Knallert_name LIMIT $rowstart,$itemsperpage");
        $numrows = dbrows($result);
        $i = 1;
        while ($data = dbarray($result)) {
            $dateposted = strftime("%d.%m.%y", $data[Knallert_datestamp]+($settings[timeoffset]*3600));
            if ($data[Knallert_datestamp]+604800 > time()+($settings[timeoffset]*3600)) {
                $new = " <span class=\"small\">[NEW]</span>";
            } else {
                $new = "";
            }
            echo "<a href=\"$PHP_SELF?cat_id=$cat_id&Knallert_id=$data[Knallert_id]\" target=\"_blank\">".stripslashes($data[Knallert_name])."</a>$new<br>\n";
            if ($data[Knallert_description] != "") {
                echo stripslashes($data[Knallert_description])."<br>\n";
            }
            echo "<span class=\"small\"><font class=\"alt\">Skrevet:</font> $dateposted | <font class=\"alt\">Visits:</font> $data[Knallert_count]</span>\n";
            if ($i != $numrows) {
                echo "<br><br>\n";
            } else {
                echo "\n";
            }
            $i++;
        }
        closetable();
        if ($rowstart >= $itemsperpage) {
            $start = $rowstart - $itemsperpage;
            $prev = "<a href=\"$PHP_SELF?cat_id=$cat_id&rowstart=$start\" class=\"white\">Forrige</a>";
        }
        if ($rowstart + $itemsperpage < $rows) {
            $start = $rowstart + $itemsperpage;
            $next = "<a href=\"$PHP_SELF?cat_id=$cat_id&rowstart=$start\" class=\"white\">Næste</a>";
        }
        if ($prev != "" || $next != "") {
            $current = "Page $currentpage of $totalpages";
            tablebreak();
            prevnextbar($prev,$current,$next);
        }
    } else {
        echo "Ingen Knallerter er blevet tilføjet i denne kategori\n";
        closetable();
    }
}
tablebreak();
echo "</td>
<td width=\"10\"></td>
<td width=\"170\" valign=\"top\" class=\"srborder\">\n";
require "userinfo.php";
require "poll.php";
require "shoutbox.php";
echo "</td>
</tr>
</table>\n";

require "footer.php";
?>