There was an odd issue with MathJax.org that provides processing for our formulas in the tests. The site was unavaialble to users in Europe and potentially other countries.... it is available in the US as we have recently checked.
We have changed the processing of the formulas ans switched it to take place locally on our server (by installing a local version of the math processing engine). It has been done about 45 mins ago and should resolve any challenges that users have had due to the DNS issue with Mathjax.org
There is a slight side effect - since we are processing formulas locally, the first time they are displayed it will take a bit more time (about one second to convert and render them). Once they have been displayed, however, they will be cached and further users will be able to see them instantly without any delay.
Please let me know if it is still not working for you.
Sorry about the issue.
BB