How to connect to iCloud?
I have recently updated to El Capitan. I keep getting a window "This Mac can't connect to iCloud because of a problem with "my e-mail address". The window gives me two choices: Later and Go to iCloud Preferences. If I go to iCloud preferences, it asks me to enter my password. When I enter my password, the computer grinds away and eventually returns "an unknown error occurred".
I am absolutely sure about my password.
What should I do to connect to iCloud?
iMac (21.5-inch Late 2009), OS X El Capitan (10.11), Can't connect iCloud Apple ID