Following an upgrade from Magento 1.5 to 1.7 the error:
Invalid backend model specified: customer_entity/address_attribute_backend_region
occurs during customer address edit or checkout address entry.
This is because in the eav_attribute table, backend_model values are incorrect. Fix with the following SQL:
UPDATE `eav_attribute` SET `backend_model` = ‘customer/entity_address_attribute_backend_street’ WHERE `attribute_code` =’street’ LIMIT 1 ;
UPDATE `eav_attribute` SET `backend_model` = ‘customer/entity_address_attribute_backend_region’ WHERE `attribute_code` =’region’ LIMIT 1 ;