Starting September 3rd, Cineversity system has changed to a new login system, based on your My Maxon account. You will be able to log into Cineversity using your email and password for My Maxon.
Not sure if this will resolve your issue. But the majority of users that are having difficulty logging into Cineversity “inside C4D” is referring to the CV-Toolbox in R20 or lower.
CV-Toolbox no longer works with R20 or lower due to the new My Maxon system. If you still need these plugins on these older versions, you can download them individually on their “Download and Install” tutorials.