Notice : A session had already been started - ignoring session_start()

Error in session declarations.
Possible reasons
1)Session is already started and you are trying to start it again
  ie, session_start() is called more than once.
2)session.auto_start may be enabled in your php.ini file.
  So if you call session_start() again it will throw an error.
 You can verify this in php.ini file or run a test file which echo phpinfo().