No real easy fix. I suggest you do not disable it.
Please read on Fabians blog more: http://blog.fabian-blechschmidt.de/mage_weee-and-why-it-is-important-for-tax-calculation/
The error is: Notice: Trying to get property of non-object in app/code/core/Mage/Core/Model/Config.php on line 1239.
Digging deeper MageCoreModelConfig would like to access `Mage::helper('core')->()` to display you the error message that Mage[Bundle|Rating|Review|Wishlist|Usa] requires the module Mage_XmlConnect. The notice message appears because the core helper is not yet initialized.
So deactivating Mage_XmlConnect works out as the solution. It has many dependencies. Btw: Only if you have the Magento own mobile app you'll need the XmlConnect module. I'll disable it every time.
If you have disabled and or removed that module you may ran into issues like this:
Warning: include() [<a href='function.include'>function.include</a>]: Unable to access
Mage/Giftmessage/Block/Adminhtml/Product/Helper/Form/Config.php in .../lib/Varien/Autoload.php on line 93
The reason is a typo in the frontend_input_renderer column in
table catalog_eav_attribute for attribute code gift_message_available.
Magento defaults this value during GiftMessage setup: giftmessage/adminhtml_product_helper_form_config
which results later in the class name Mage_Giftmessage_Block_Adminhtml_Product_Helper_Form_Config but the folder
name is app/code/core/Mage/GiftMessage. The upper and lower M.
Solution
If you disable GiftMessage module before installing the Mock Module then the Mock installer will
correct the name of the input renderer to giftMessage/adminhtml_product_helper_form_config.
If you disable GiftMessage after the installation then please either drop/remove yourself
the attribute gift_message_available or simply run this:
UPDATE `catalog_eav_attribute`
SET xfrontend_input_renderer=''
WHERE `attribute_id` = (SELECT attribute_id FROM `eav_attribute` WHERE attribute_code = 'gift_message_availablee')
The typos in the SQL query are on purpose so that you hopefully read this before proceeding.
The better way is to create an install script in one of your app/code/local/ modules to
change/remove the attribute gift_message_available.