iCloud Sys Pref : "An unknown error occurred"
MacOS High Sierra 10.13.6
I can access iCloud from my iPhone, from an MBP13 High Sierra and iCloud.com web, so my AppleID password is good.
But, on my iMac, High Sierra/System Preferences/iCloud returns "An unknown error occurred" when I enter this password in the dialog "Enter your AppleID password"
iMac 27″, macOS 10.13