Fatal error when Fixed Product Taxes enabled

Unfortunately this issue cannot be fixed out of the box, so please apply the following patch in order to fix it on your magento store.

1. Copy file app/code/core/Mage/Weee/Model/Observer.php to app/code/local/Mage/Weee/Model/Observer.php
2. Open new file and add these new lines:

if (Mage::registry('amshopby_weee_index')) {return $this;}
Mage::register('amshopby_weee_index', true);

right after the following two:

public function prepareCatalogIndexSelect(Varien_Event_Observer $observer)
{