MappingException: The class 'Acme\UserBundle\Entity\User' was not found in the chain configured namespaces

MappingException: The class 'Acme\UserBundle\Entity\User' was not found in
the chain configured namespaces

I need to use etity_managers instead of auto_mappings
it shows this error.
MappingException: The class 'Acme\UserBundle\Entity\User' was not found in
the chain configured namespaces
my config.yml is like this.
doctrine: dbal:
orm:
auto_generate_proxy_classes: %kernel.debug%
entity_managers:
FOSUserBundle: ~
FOSMessageBundle: ~
AcmeUserBundle: ~
Is there anything I have to do ?