answer you (taken from another popular forum), I quote:
"You have a device which has already created three iCloud accounts and therefore can't create any more.
So you go to another iOS device or Mac and create a new iCloud account there.
Then you go back to the first device and sign into to the iCloud pane with the ID of the account you just created."
Thank you, 3 icloud account should be enough for an ios device, and might not be enough for a mac used by multiple users, by using a account created on another device could solve the problem.