php extension mcrypt must be loaded

Hope your system is ubuntu as you added the tag.

On Ubuntu when you run sudo apt-get install php5-mcrypt it doesn't actually install the extension into the mods-available. You'll need to symlink it.

sudo ln -s /etc/php5/conf.d/mcrypt.ini /etc/php5/mods-available/mcrypt.ini

Then enable the extension and restart Apache.

sudo php5enmod mcrypt
sudo service apache2 reload