"Request Not Supported" Message

My student encountered a "this request is not supported" error message while working on the pretest. Why did this happen?

This occurs when our site logs users out after a certain time period of what seems like inactivity. For security reasons, our site automatically logs users out after several minutes of what seems like inactivity. The vast majority of students are able to complete the pretest quiz as well as most full-length quizzes before this security measure affects them.