One thing that may be contributing to this is the presence of spaces and a potentially restricted character (the dash) in the file paths. Remedy this for your Flow Direction Grid by adding underscores to Neuer Ordner where there are spaces and just to be safe remove the dash. Check all your other data to see if this is an issue.
Raster processes have much more specific file naming conventions than typical GIS files, so this could be what is causing the problem. Unfortunately, there is not an explicit error that will come up advising the user that spaces and restricted characters are present and therefore causing a problem.
Output raster formats and names—ArcGIS Help | ArcGIS Desktop
Chris Donohue, GISP