Today I learned something, thank you. Is this a freshly installed server? Than this might be your issue, too: The server simply had insufficient entropy to create the initial setup token.
After following this answer, SCM-Manager started successfully. Simply install “rng-tools” and run them once:
sudo apt-get install rng-tools
sudo rngd -r /dev/urandom
Then restart SCM-Manager. I would love to hear whether this works for you 