Проблема решена следующим образом:
Закомментировал строчку
<!--<a tab="#tab_related"><?php echo $tab_related; ?> (<?php echo count($products); ?>)</a>-->
в файле catalog/view/theme/default/template/product/ product.tpl
Так же в div tab_description добавлен div tab_telated
<div id="tab_description" class="tab_page"><?php echo $description; ?>
<div id="tab_related" class="tab_page">
<div align="left">
<H2><font color="#CC0000"> C этим товаром также покупают: </font></H2>
</div>
<?php if ($products) { ?>
<table class="list">
<?php for ($i = 0; $i < sizeof($products); $i = $i + 4) { ?>
<tr>
<?php for ($j = $i; $j < ($i + 4); $j++) { ?>
<td width="25%"><?php if (isset($products[$j])) { ?>
<a href="<?php echo str_replace('&', '&', $products[$j]['href']); ?>"><img src="<?php echo $products[$j]['thumb']; ?>" title="<?php echo $products[$j]['name']; ?>" alt="<?php echo $products[$j]['name']; ?>" /></a><br />
<a href="<?php echo str_replace('&', '&', $products[$j]['href']); ?>"><?php echo $products[$j]['name']; ?></a><br />
<span style="color: #999; font-size: 11px;"><?php echo $products[$j]['model']; ?></span><br />
<?php if ($display_price) { ?>
<?php if (!$products[$j]['special']) { ?>
<span style="color: #900; font-weight: bold;"><?php echo $products[$j]['price']; ?></span>
<?php } else { ?>
<span style="color: #900; font-weight: bold; text-decoration: line-through;"><?php echo $products[$j]['price']; ?></span> <span style="color: #F00;"><?php echo $products[$j]['special']; ?></span>
<?php } ?>
<a class="button_add_small" href="<?php echo $products[$j]['add']; ?>" title="<?php echo $button_add_to_cart; ?>" > </a>
<?php } ?>
<br />
<?php if ($products[$j]['rating']) { ?>
<img src="catalog/view/theme/default/image/stars_<?php echo $products[$j]['rating'] . '.png'; ?>" alt="<?php echo $products[$j]['stars']; ?>" />
<?php } ?>
<?php } ?></td>
<?php } ?>
</tr>
<?php } ?>
</table>
<?php } else { ?>
<div style="background: #F7F7F7; border: 1px solid #DDDDDD; padding: 10px; margin-bottom: 10px;"><?php echo $text_no_related; ?></div>
<?php } ?>
</div>
</div>