If you are noticing the above error in Apache error logs and having problems for login scripts the problem is with post_max_size variable in php.ini
Here is what you need to do, Find out the correct php.ini configuration file.
root@server [/usr]# php -i | grep php.ini
Configuration File (php.ini) Path => /usr/local/lib
Loaded Configuration File => /usr/local/lib/php.ini
Edit the loaded php.ini file and check for post_max_size variable value, Set it to 8M which is best recommended.
root@server [/usr]# grep post_max /usr/local/lib/php.ini
post_max_size = 8M
Then restart Apache, That should resolve the problem.