Class 'SimpleXMLElement' not found on puphpet PHP 5.6
The problem was that I was using Cent OS and in this Linux Distribution, the
php-libxml package does not come as default.
I ended up generating a new machine through PuPHPet GUI and added to the System Package the following packages to be installed:
For those using PHP 7 and Ubuntu, @MPS solved it by running
apt-get install php7.0-xml and
service apache2 restart.