Found another error that we see a lot that I wanted to put check out there for you to know:
The error "another user is currently logged in" occurs when the attributes sent in the SAML assertion do not match the email address that was used to start the login process.
Check the attributes in the SAML assertion and make sure that they are an exact match to the ID the user is attempting to use, and also an exact match with the Admin Console. - How to perform a SAML Trace
Chances are the Email address is what is causing the problem or you have something funny with the user's name.
I have been using CC through my college for a few years with no issues.
my Attribute Name=\"Email\ in the saml is now using a different email
(I have applied to go back to university, and the university email is showing up)
But the college uses outlook and the university uses gmail.
I get the "another user" error message, as it makes sense, i start the session with a college email then later it's a university email.
This is way beyond my ability to understand, but it was working at 10am and after i rebooted it stopped working and started giving me this error (happens on the web log in and on the program log in) This email has both a personal and a school log in.