after upgrade my xubuntu distro (64bit) 17.04 to 17.10, i have reinstalling sync desktop client , through ppa, but after login in the app (username and password are correct) the app icon in the panel became red with an X and when i opening the setting window appear an error message: “Could not read system exclude file”
I got the same error.
In my case, it was because the file
sync-exclude.lst was missing at /etc/Nextcloud.
And, I don’t know why, it was not created with the reinstall of the desktop application.
You can look at https://github.com/nextcloud/desktop/issues/172 for more details.