1. Create a php file with <?php phpinfo(); ?> and open it with your browser.
2. Look for Loaded Configuration File (this shows the actual conf. file in use) and edit upload_max_filesize and set post_max_size to the same value (or make it 0 to disable limit) in that file in root mode.
3. Execute: sudo service apache2 restart

I had the same problem running on a virtual server. Turns out that /var/lock is a symbolic link to /run/lock, which didn't exist. I solved it like this:

sudo mkdir /run/lock

Then restart Apache:

sudo service apache2 restart

Hope it works for you.