Yesterday I uninstalled and reinstalled the whole Automation Studio (6.5.2.12 SP) but that didn’t help.
Before that, I reinstalled the DTM 2.1.1.2 from the website B&R DTM | B&R Industrial Automation
I tried to open an old project with AS4.12 where also a Profinet card is in use.
AS4.12 shows the same behaviour as AS6 with my new project.
Something is wrong on my PC. On other machines I can open the projects without problems…