The error occurred in the first section of the test only when an email link is supplied to go to the first batch of questions. Clicking on the link in the email produced an empty web browser. No error codes or messages.
We found that if pupils went onto the next task and left the web browser open, they might get the page later - much later.
Those that got that far sometimes managed to get one of the linked question pages but not all.
All other links to web pages elsewhere in the test all worked fine.
In some downtime, I tried one of the practice tests and had a similar fault although it varied according to which level I was entered for!
In previous posting I mentioned Browse Control. I removed this from one room's PC for the afternoon. It made no difference in a practice test.