how to configure extproc in listener.ora on 11gR2 RAC ?

configure listener with netca ,and add extproc with netmgr, but raise error:
SQL> select spkg.encrypt(rawtohex('a')) from dual;

select spkg.encrypt(rawtohex('a')) from dual

ORA-28595: Extproc agent : Invalid DLL Path
ORA-06512: at "ADMIN.SPKG", line 6377

1:RAC env:
      11gR2,redhat linux 5 ,x86-64

2: listener.ora

ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER_SCAN1 = ON

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (PROGRAM = extproc)
      (ENV = 'EXTPROC_DLLS=ANY')
      (SID_NAME = PLSExtProc)
      (ORACLE_HOME = /opt/11.2.0/grid)
    )
  )

LISTENER =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = IPC)(KEY = LISTENER))
  )

ADR_BASE_LISTENER = /opt/11.2.0/crs

ENABLE_GLOBAL_DYNAMIC_ENDPOINT_LISTENER = ON

LISTENER_SCAN1 =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = IPC)(KEY = LISTENER_SCAN1))