$sql = "SELECT SQL_CALC_FOUND_ROWS img, nombre, dur, id FROM videos where cat + cat2 = 'Rubias' order by id desc LIMIT $offset, $limit"; 

$sql = "SELECT SQL_CALC_FOUND_ROWS img, nombre, dur, id FROM videos WHERE cat1 = 'Rubias' OR cat2 = 'Rubias' order by id desc LIMIT $offset, $limit"; 

Warning: mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource in /home2/rapmadri/public_html/tupixxx/lista3.php on line 37

<?php 
         while ($row = mysql_fetch_assoc($rs)) 
         { 
            $name = $row["img"]; 
			$id = $row["nombre"]."";
			$dura = $row["dur"]."";  
			$url = $row["id"];
         ?>
<div style="float: left;">
<?php