ERROR :: Fatal error: Call to a member function addCacheTag() on a non-object in public_html/app/code/core/Mage/Catalog/Model/Observer.php on line 215 you can find the lines 241 :: $menuBlock->addModelTags($categoryModel); 215 :: $block->addCacheTag(Mage_Catalog_Model_Category::CACHE_TAG); here is not error fixing place in block class is " Mage_Page_Block_Html_Topmenu " you can find getHtml function in that you can see Mage::dispatchEvent('page_block_html_topmenu_gethtml_before', array( 'menu' => $this->_menu )); replace above code to below code Mage::dispatchEvent('page_block_html_topmenu_gethtml_before', array( 'menu' => $this->_menu, 'block' => $this //add this line ));