The 5 or more computers limitation usually refers to the number of devices authorized for the content, i.e. the number of computers authorized with your AppleID.
Follow this procedure: https://discussions.apple.com/thread/4002746?start=0&tstart=0
Deauthorize all your computers and then authorize the one you want authorized. See:
If you authorized a computer and then the hard disk crashed and you reinstalled the operating system, the crash hard disk is still authorised.