There is a fatal error while extension running

if you're running several extensions there may be a fatal error because of their conflict.

Please, perform the next actions, which may help to you:

Open

app\code\local\Amasty\Conf\Model\Observer.php

and delete the following:

if (!is_null(Mage::registry('product')))
{
Mage::unregister('product');
}
Mage::register('product', $_product);