ORA-12528, Blocked, all appropriate instances are blocking new connections.

UR=A Connecting to Oracle Instance OPEN in Restricted Session

To connect to instance running in restricted mode, add the UR = A clause under the CONNECT_DATA parameter of the tnsnames. ora file:

(CONNECT_DATA=

(SERVICE_NAME = PRD1.de.jnb.com)
(UR = A)
)

sqlplus ‘sys/**********@prd1 as sysdba’

ORA-12528, Blocked, all appropriate instances are blocking new connections.