We were able to connect to the MySQL database server (which means your username and password are okay) but not able to select the database.
The MySQL error was: Access denied for user: 'dbo211455680@%' to database 'db211455680'.
Currently, the database is db211455680. The username is dbo211455680 and the database server is db1005.1und1.de:3306.
For more help, see the Installation and upgrading handbook. If you are unsure what these terms mean you should probably contact your hosting provider.