How can I fix this error?
There has been an error processing your request
Invalid backend model specified: improvedapi/catalog_category_attribute_backend_tags
Trace:
#0 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Eav/Model/Entity/Attribute/Abstract.php(346): Mage::exception('Mage_Eav', 'Invalid backend...')
#1 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Eav/Model/Entity/Abstract.php(640): Mage_Eav_Model_Entity_Attribute_Abstract->getBackend()
#2 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Eav/Model/Entity/Abstract.php(1641): Mage_Eav_Model_Entity_Abstract->walkAttributes('backend/afterLo...', Array)
#3 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Eav/Model/Entity/Abstract.php(964): Mage_Eav_Model_Entity_Abstract->_afterLoad(Object(Mage_Catalog_Model_Category))
#4 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Catalog/Model/Resource/Abstract.php(698): Mage_Eav_Model_Entity_Abstract->load(Object(Mage_Catalog_Model_Category), 0, NULL)
#5 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Core/Model/Abstract.php(225): Mage_Catalog_Model_Resource_Abstract->load(Object(Mage_Catalog_Model_Category), 0, NULL)
#6 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Adminhtml/controllers/UrlrewriteController.php(57): Mage_Core_Model_Abstract->load(0)
#7 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Adminhtml/controllers/UrlrewriteController.php(68): Mage_Adminhtml_UrlrewriteController->_initRegistry()
#8 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Core/Controller/Varien/Action.php(418): Mage_Adminhtml_UrlrewriteController->indexAction()
#9 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Core/Controller/Varien/Router/Standard.php(254): Mage_Core_Controller_Varien_Action->dispatch('index')
#10 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Core/Controller/Varien/Front.php(172): Mage_Core_Controller_Varien_Router_Standard->match(Object(Mage_Core_Controller_Request_Http))
#11 /var/www/clients/client1/web1/web/site/app/code/core/Mage/Core/Model/App.php(365): Mage_Core_Controller_Varien_Front->dispatch()
#12 /var/www/clients/client1/web1/web/site/app/Mage.php(684): Mage_Core_Model_App->run(Array)
#13 /var/www/clients/client1/web1/web/site/index.php(94): Mage::run('italiano', 'store')
#14 {main}
