The problem occurs after the message asking to set up a password recovery option (see the figure attached). If I click to set recovery, I can enter into my account preferences (not the application status page) without any problem. However, if I click "not now", I get the login error, not able to check my application status...
I asked it on reddit (r/gradadmissions) and there is two more applicants with this same problem (login error E999).
I will wait until tomorrow before contacting grad-admissions. Thanks for your reply!