Cannot logout or change settings in iCloud - OS X 10.11

I have tried this but it won't let me turn off mail and if I can't do that, it won't let me sign out. Any ideas?

Didn't work for me, but I solved the issue by deleting tons of stuff from User/Library/

https://discussions.apple.com/message/27731633#27813443

After that I could delete the accounts from Internet Accounts and sign back in.

Boom. Worked like a charm.

Thanks!

After step 1, I get a message telling me to turn off the various iCloud services first in order to log off of iCloud. But the checkboxes to turn off the services are all greyed out, so they can't be turned off.

I'm going to try deleting the folder in ~/Library, suggested below by Max108

I've been having the same issue but when I go to: /Users/<MY HOME FOLDER>/Library/Application Support there is no icloud folder!

Just to rule out the possibility, please confirm that the Library/Application Support folder you are looking in is the ~/Library (in your user folder) and not the //Library (in the root directory), because both libraries have Application Support folders.

I had the same problems, but for me all solutions mentioned above did not help. Every time I tried to connect to iCloud I received a message: 'U kunt niet verbinden met iCloud vanwege een onbekende fout' (you cannot connect to iCloud due tuo an unknown error)

What DID help was changing the language in SYstem Preferences from Dutch to English, after that my iCloud-problems were gone (even after I changed the language back to Dutch)