I have a user with a German umlaut in it's user ID. You will get the following error message when trying to log in:
Error: Registration/Login of the user does not work.
If you create a user with the “Copy user” option, it is possible to use German umlauts like ä, ö, ü, ß. for the user ID. However, as soon, as there is a German umlaut in the user-ID in the dwuser table of the database, you cannot log in to the DocuWare Windows Client anymore. In order to be able to log in again, it is necessary to either recreate the user or to manually delete any umlaut from the column dwuid in the table dwuser, which you can find in the dwsystem database.