There can be different causes why you are unable to log in. Please check the following points thoroughly:
Did you receive the registration key from the administration?
Please check if you really have completed the registration successfully. Only after completing the registration you can log in with your email adress and account password.
Are your login credentials correct?
Please check for typos and check the uppercase lowercase writing.
You have checked these points but still can’t log in?
You can find further information in our article Login not possible.