I have a classmate that just recently has been unable to login. The classmates profile has only 1 email and that has not changed and I have verified that is correct and I can send email to this email address. I have changed the password and sent her the new password and she still can't login. I have changed the password again and then tried to login under the classmate using the classmates email and new password and I can't login either. I'm getting an error: " Invalid Login or Password. REMEMBER that you can only use your primary email address to log in. Please try again."

I am using the primary email and 6 alphanumeric character password

Any suggestions of how to resolve?

Since you've eliminated the password, all that's left is the email address - which you say looks good and should be valid. But I've seen things like failing passwords and email addresses which somehow ended up looking good but contained a non-displaying character.

Make a note of the original email address, and replace it with something simple like abc@def.com. The email address doesn't have to be valid to log in with - it just has to be the correct format. Try logging in with the new email address and password. If that works, put the old email address back and try logging in again using that. Unless there's some character in the original email address that CC is not accepting in the login process, you should be good to go.