Oracle Solution for Error ora-12522

ORA-12522: TNS:listener could not find available instance with given INSTANCE_ROLE

What triggered the Error:

There are not any available and appropriate database instances registered with the listener, that are part of the service identified by SERVICE_NAME given in the connect descriptor and that have the specified INSTANCE_ROLE (and INSTANCE_NAME, if specified).

What should we do to fix it:

Check to make sure that the INSTANCE_ROLE specified is correct. Run "lsnrctl services" to ensure that the instance(s) have registered with the listener and that they are ready to accept connections.