Can't enable iCloud Drive on OS X Sierra

Solution 1:

In case this is your company's computer, it could have been deactivated through a management software, like jamf:

https://www.jamf.com/jamf-nation/discussions/20997/disable-icloud-desktop-and-documents-in-sierra

Solution 2:

These ports need to be open on your company's firewall/security appliance to allow iCloud in general:

To allow iCloud to function, Apple has a list of ports which need to be allowed for iCloud to function on your client devices. The ports used by iCloud are:

TCP 25

TCP 80

TCP 443

TCP 587

TCP 993

TCP 5223

See this Meraki page for more details. Your company's IT group should be able to tell you if these ports are blocked. Which specific port blocks iCloud Drive is not clear.