Yeah me too. Same ID all this time since they had IDs. Several devices and desktops using it. But I also created an iCloud address. It's attached to the same ID. Also when you sign up for iCloud (on a device) you are forced to create an iCloud address. At least I was.
I'm signed in right now on a new Mac mini. Shouldn't have this message.
wow.. I had to delete the "Install OSX Mavericks" dmg image from my Mac. Now it works.