Oracle Solution for Error ora-12527

ORA-12527: TNS:listener: all instances are in restricted mode or blocking new connections

What triggered the Error:

All appropriate database instances supporting the service requested by the client reported that they either were in restricted mode or were blocking the new connections. The Listener does not allow connections to such instances. This condition may be temporary, such as at instance startup.

What should we do to fix it:

Attempt the connection again. If error persists, then contact the database administrator to check the status of the instances.