iMessage Registration?

Has anyone seen this message before? I was given an older iMac (2010) which works great, but when I try to login to iMessage and FaceTime I got the following message:

iMessage Registration

Apple needs more information to complete your iMessage registration. Please call AppleCare in your country (listed below) and provide them with the following validation code:

xxx-1291-4542

When I called them they said I had to purchase some support membership.