Hi Bruno,
I've found the problem with the help of the apple support.
For all of you, who has the same Problem:
First Solution (worked for me):
- deactivate Little Snitch and start Mainstage again.
Second Solution
- Go To "Library" using the upper Menu "Go To" -> Press Alt to see the "Library"
- Open Caches Directory
- Put all of the directories (in Caches) in to the trashcan
- Shutdown your Mac (without cleaniing your trash)
- Press Left Shift und Start Mac (It will start in Secure Mode)
- After the start, clean your trashcan
- Shutdown your Mac again
- Start your Mac and press immediately CMD + R + P
- Wait until your mac starts 2-3 times
This procedure will clean your cache and some other things. Doesn't worked for me, but could be useful for some others.
Best Regards
Mahzuni