OK, we worked out what the problem was there, we needed to download a patch and install.
I have set everything up, invited the students, and given them permissions. I have selected a couple of students and supervised them through the set up process and all they get is a blank screen with the ability to log off.
I can't see what I have done wrong. I have also noticed that the invitation setup has chnaged from last year. I can't find any instructions online and I am at a loss. Can anyone help?