Hi!
Thank you for reaching out to our community! Knowing how the student is logging in, whether it is via Canvas, Student Portal, or using the Test ID, would help to determine what the issue may be. I would recommend that you submit a support ticket to let them know which student is having the issue, the name of the tracker, the name of the assessment, and the way the student is accessing the assessment.
How do I create a Mastery Connect support ticket?
Also, if you need the student to take the assessment prior to this being solved, have them go to student.masteryconnect.com and enter the Test ID and the student ID.
How do I deliver a formative assessment to students?