Sometimes when teachers log into the assessment site or try to create an assessment, they receive an "Invalid request" message.
We have seen this particular problem show up and we are still trying to debug this problem.
However, what seems to fix the situation for most people is to completely log out of both the assessment site and the eBook, close your browser, and clear your cache. Then begin again. This usually makes that “invalid request” error go away.
Please give this a try. If it still persists, check if it happens on both a home computer and school computer. Some schools have security features such as firewalls that cause problems with the site. If it only happens on one computer and not the other, it is probably a security feature on your home computer or on your school computer that will need to be adjusted on your end.