ORA-12518: TNS:listener could not hand off client connection ORACLE XE 11.2 x64 I'm starting to become very very frustrated by Oracle.
So, I have Oracle XE 11.2 64 bit and ODAC121012_x64 installed.

I can start listener; I can do tnsping xe; but when I try to connect as via sqlplus as system I'm getting:

ERROR:
ORA-12518: TNS:listener could not hand off client connection


Here are my config files:

tnsnames.ora:

XE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = XE)
    )
  )

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) 
    ) 
  ) 


listener.ora:

SID_LIST_LISTENER =
  (SID_LIST =
     (SID_DESC =
                           (SID_NAME = XE)
       (ORACLE_HOME =  C:\oraclexe\app\oracle\product\11.2.0\server)
     )

    (SID_DESC =
      (SID_NAME = PLSExtProc)
      (ORACLE_HOME = C:\oraclexe\app\oracle\product\11.2.0\server)
      (PROGRAM = extproc)
    )
    (SID_DESC =
      (SID_NAME = CLRExtProc)
      (ORACLE_HOME = C:\oraclexe\app\oracle\product\11.2.0\server)
      (PROGRAM = extproc)
    )
  )

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1))
      (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))
    )
  )

DEFAULT_SERVICE_LISTENER = (XE)


sqlnet.ora:

# This file is actually generated by netca. But if customers choose to 
# install "Software Only", this file wont exist and without the native 
# authentication, they will not be able to connect to the database on NT.

SQLNET.AUTHENTICATION_SERVICES = (NTS)


Help is very much needed and will be even more appreciated!
To understand the problem and try to fix it you need to check related logs: 
 listener.log, alert log, trace file, etc

possible causes and solutions:


listener problem:


Make sure there is no error message and listener is up and running by execute the following command:

lsnrclt status


if listener is down check the following it may help you troubleshoot this issue:


could be network error: check the even log for any network error and fix them.
service stopped or it has failure when trying to start:  start---&gt;run---&gt;services.msc the search for oracle listener service  should be like OracleInstancename  try to start it, if it failed to start it will throw an exception inside listener error and windows error number. please provide that error


listener workaround: 

add the following parameter to your listener:

DIRECT_HANDOFF_TTC_LISTENER=OFF





database problem:


1.database server memory were enough for new connection


database connection parameters such as: dedicated server, please checked processes parameter or query from v$resource_limit where resource_name=’processes’; checked max_utilization must less than Limit_value or shared server, verify large_pool_size or check dispatcher were enough for all connection.