I get the above error when I try to save from many pages, such as Settings, Episode Naming.
It’s a new install of 2.0.0.2850 on Windows 8.1x64.
Settings do save some of the time.
Things seem to have come right after a couple of reboots. Haven’t seen this message in my current session and I’ve saved lots of settings.
Restarting Sonarr seemed to solve my problem, thanks.