Unable to log errror in php log file

Hello Friends,
Well I'm not sure what exactly am I missing. Though the errors are displayed on my web pages they are not logged in my error log file that is specified in php.ini file.

Here is the setting of the php.ini file for it.

**************************************************

error_reporting = E_ALL

display_errors = On

display_startup_errors = On

log_errors = On

; Log errors to specified file.
error_log = c:phperror.log

************************************************** *

Please help me solve this problem.
Thank you