You have probably received a new user account at Universität Hamburg because you have been away from Universität Hamburg for some time. However, the e-mail address is generated according to the scheme
firstname.surname@uni-hamburg.de. Usually, even the matriculation number is retained.In Moodle and probably also in other systems, however, your old user account still exists. The system does not allow multiple accounts to share the same e-mail address. Therefore, you cannot log in at the moment.
Please contact our support so that we can either deactivate the old account or merge it with your new one.