Article doesn't show on registration AJAX REGISTER

On my registration-page the article which shows the terms of use doens't show. a window is popping up, but remains white/blank.
tested this on different browsers with different articles. always the same problem 

my registration page: www.phmaterial.ch/index.php/registration-2
thanks for your help

Hello,

The URL of the article /index.php/component/content/article?layout=modal&id=24&tmpl=component is a blank page. You should activate error reporting to see what's wrong.