ORA-12528: TNS:listener: all appropriate instances are blocking new connections

When database are in mount mode or restricted session enabled you'll get this error since 10g.

There are two way to get around it.

1. Put UR=A in your tnsnames.ora for the entry. e.g.
   

   STBY=
    (DESCRIPTION =
      (ADDRESS_LIST =
        (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
      )
      (CONNECT_DATA =
        (SERVICE_NAME = STBY)
        (UR = A)
      )
    )
   

   
   
2. Create static listener to allow listener know which oracle SID to connect. e.g.
   SID_LIST_LISTENER =
   (SID_LIST =
   (SID_DESC =
   (GLOBAL_DBNAME = TESTDB.gov.edmonton.ab.ca)
   (ORACLE_HOME = /u01/app/ora10g/product/10.2.0.4/db_1)
   (SID_NAME = TESTDB1)
   )
   )
   After you change listener.ora you need reload listener to take effect.