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

Question

Hi when trying to create Repository Creation Utility by Data Connection details are not excepting.it throws the Exception is

Listener refused the connection with the following error:
ORA-12528, TNS:listener: all appropriate instances are blocking new connections

tnsnames.ora

XE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = sivanagendra-lap)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = XE)
    (UR = A)
    )
  )

EXTPROC_CONNECTION_DATA =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1))
    )
    (CONNECT_DATA =
      (SID = PLSExtProc)
      (PRESENTATION = RO)
    )
  )

ORACLR_CONNECTION_DATA = 
  (DESCRIPTION = 
    (ADDRESS_LIST = 
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1)) 
    ) 
    (CONNECT_DATA = 
      (SID = CLRExtProc) 
      (PRESENTATION = RO) 
    ) 
  ) 

Please give me solutions on this issue.

Answer 1

Possible reasons

1. Is database in restricted mode?
2. Is database not mounted? Or maybe starting up? If the latter, then it could be a temporary problem - wait until it is fully started up.
3. For shared connections it could be that all shared servers are busy. For dedicated connections it could be that Processes or Sessions parameter are too low. Or maybe you're hitting some OS limitations/settings (eg. one of ulimits).