Just in case anyone else has the same problem this partially fixed the problem. The additional images now show in Lightbox but the next and previous buttons are working but at least it's workable. Added below to tpl_modules_additional_images.php thanks to Brandon Walters
require(DIR_WS_MODULES . zen_get_module_directory('additional_images.php'));
?>
<?php
if ($additional->RecordCount() > 0) {
?>
<div id="productAdditionalImages">
<!-- Fix for broken click to enlarge - Brandon Walters http://www.bwaltdesigns.com -->
<?php
while(!$additional->EOF) {
echo '<div class="additional-images"><a href="images/' .$additional->fields['additional_image']. '" rel="lightbox">'.zen_image(DIR_WS_IMAGES . $additional->fields['additional_image'], '', ADDITIONAL_SMALL_IMAGE_WIDTH, ADDITIONAL_SMALL_IMAGE_HEIGHT).'</a></div><br/>';
$additional->MoveNext();
}
?>
</div>
<?php
}
?>