Hi,
I am glad you have figured that out by yourself. For those you suffer this problem;
You needed to install the DOM extension to your hosting. If you are using a dedicated or VPS hosting, you can do this by yourself via:
on debian/ubuntu using:
sudo apt-get install php5-dom
And on CentOS:
Or alternatively you can contact to your hosting provider support desk and have them to do it for you (which is recommended)
Case solved. Topic is closed.
Regards.