The set coordinate system (i.e. some projected coordinate system) does not match the network objects' coordinate values (i.e. meeting a geographic coordinate system, thus showing degree values). How can I solve this?
In Network -> Network settings -> Scale -> Coordinate system the declared coordinate system has been saved. ('Visum' means that no coordinate system was declared.) Choose the correct coordinate system, for example WGS84: Geographic Coordinate Systems -> World -> WGS 1984.
Klick OK and uncheck the option 'Transform coordinates in case of changes'. This will declare the coordinate system to meet the real network object coordinates.