I am trying to display the manufacturer's other product link on the product page instead of inside the Manufacturer sidebox.

This is the code I am using:
PHP Code:
<?php echo '<a href="' . zen_href_link(FILENAME_DEFAULT, 'manufacturers_id=' . $_GET['manufacturers_id']) . '">' . zen_image(DIR_WS_TEMPLATE_IMAGES . BUTTON_IMAGE_OTHER_MANUFACTURER, BUTTON_OTHER_MANUFACTURER_ALT) .'</a>'; ?>
Unfortunately it doesn't work, it generates the url without the manufacturer id.

Help please!