Error 12154 received logging on to the standby happening on One node of Standby

 I am recieving the following error continuously on one node of my standby database.

*** 2009-10-12 16:09:06.045 61287 kcrr.c
Error 12154 received logging on to the standby
Error 12154 connecting to destination LOG_ARCHIVE_DEST_2 standby host 'nnnn'
Error 12154 attaching to destination LOG_ARCHIVE_DEST_2 standby host 'nnnn'
*** 2009-10-12 16:09:06.045 61287 kcrr.c
PING[ARC0]: Heartbeat failed to connect to standby 'nnnn'. Error is 12154.
*** 2009-10-12 16:09:06.045 59530 kcrr.c
kcrrfail: dest:2 err:12154 force:0 blast:1

listener.ora:

#ADMIN_RESTRICTIONS_LISTENER_SDB0033 = ON

LOGGING_LISTENER_SDB0033 = on

LISTENER_SDB0033 =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1))
      (ADDRESS = (PROTOCOL = TCP)(HOST = nnnn)(PORT = xxxx)(IP = FIRST))
      (ADDRESS = (PROTOCOL = TCP)(HOST = nnnnn)(PORT = xxxx)(IP = FIRST))