Yahoo! Music Unlimited Installed on 3 Computers Already; Deactivate One Computer and Replace with a New One
You must deactivate a machine running one of the three active Yahoo! Music Unlimited accounts to use Y! Unlimited on an additional machine. You may use the Yahoo! Music Jukebox on any number of machines; however, a single Y! Unlimited subscription can only be used on up to three machines. Therefore, you must manually deactivate one of the machines if you wish to access Y! Unlimited on more than three.
To do this, go to one of the active computers and start the Yahoo! Music Jukebox. Be sure you are logged in with your Y! Unlimited subscription ID. Click Edit > Preferences > Y! Unlimited, and click Deactivate under Y! Unlimited Deactivation. You will then be able to add Yahoo! Music Unlimited to another machine.