Problems with registration after reinstalling Adobe CS6

Hello, I have a computer (Mac Mini running OS X El Capitan) with Adobe CS6 Master Collection installed.
I had to reinstall the operating system and now want to reinstall the Master Collection. Unfortunately, the licensing process fails, and I get an error message saying there is no internet connection.
See screenshot.
I’ve already searched through all the help pages I could find and tried the following:
- The computer is connected to the internet
- Adobe licensing servers are reachable --> Pong
- Checked the hosts file
Unfortunately, none of this helped.
How can I solve this problem?
Thank you very much
Andreas
