Error ORA-12519, TNS:no appropriate service handler found

Why: The listener could not find any available service handlers that are appropriate for the client connection.

Solution:
Run "lsnrctl services" to ensure that the instance(s) have registered with the listener, and are accepting connections.


Source: http://www.dba-oracle.com/sf_ora_12519_tns_no_appropriate_service_handler_found.htm