Stockable plugin undefined stdClass

[sergio0187]

Hi,

My add to cart won't work for products with the stockable plugin.

I get the errror log: PHP Notice:  Undefined property: stdClass::$param in /domains/kingscreations.nl/public_html/alpaca/jupgrade/plugins/vmcustom/stockable/stockable.php on line 707, referer: http://www.kingscreations.nl/alpaca/jupgrade/activiteiten/bergsport/testsergio-detail

If I switch to default Beez template, or disable any third party plugin, it remains.

VM version 2.0.24a
Joomla version 2.5.14

Sample page: http://www.kingscreations.nl/alpaca/jupgrade/activiteiten/bergsport/testsergio-detail

Hope anyone has a clew. Thanks in front for helping out.