Please make sure that you are at the right instance, which is the instance you are originally invited to through your registered email address. It should be the campus specific instance of Gradarius (something like yourcampusname.gradarius.com) in order to login to the course. For example, if you are from Stevens Institute of Technology, you should log into the instance: https://stevens.gradarius.com
If you are in the right instance and still trouble logging in, please create a ticket here and Gradarius Support Team will get back to you as soon as possible.