How to get php error logging working properly in a production site
Just to be sure that you are in the right path...

PHP.net says that:


  Note:
  
  Although display_errors may be set at runtime (with ini_set()), it won't have any affect if the script has fatal errors. This is because the desired runtime action does not get executed. 


Also check http://www.php.net/manual/en/errorfunc.configuration.php#ini.log-errors and http://www.php.net/manual/en/errorfunc.configuration.php#ini.error-log