Something isn't right. It's not loading the category Joomla table object. This is a native table so no include is needed and should be working perfectly fine unless it was removed for whatever reason. It's failing at the below when attempting to load the category object.
Code:
$category = JTable::getInstance( 'category' );
$category->load( (int) $id );
$cache[$id] = $category;
Please disable Joomla content plugins 1 by 1 until resolved within Extensions > Plug-in Manager as it's possible there is some sort of conflict.
nant
