Replying to myself: I found a solution here: https://superuser.com/questions/198525/how-can-i-execute-a-windows-command-line-in-background.
Apparently using
start “” “C:\Program Files (x86)\Brunner Elektronik AG\CLS2Sim\CLS2Sim.exe”
does the trick. Don’t know why the empty “” makes such a difference, but at least I can continue now.
Klaus