Hi!
thanks for your help. I tried to start the calibre server on my other mac today and it worked! Then I copied all settings, restarted calibre and now it works on my laptop as well! The prefix was the thing that broke the server!
I can reproduce it: set a prefix "calibre" and browse to
http://localhost:8080/ gives the result described in my first posting.
http://localhost:8080/calibre only returns a 404.
My problem probably was, that I changed the settings and restarted the server but did not save the settings before restarting.
Anyway, it seems that the prefix-feature is broken. Not a big issue for me - I am happy to use the server without prefix as well!
Thanks for all your support - as a software developer myself, I really appreciate that!
christof