This computer is already associated with an Apple ID.

Hi folks

Looks like I'm locked out of downloading from iTunes Match for 90 days. Not sure what I've done wrong. Problem is I have all my tunes in the match cloud and none on my iMac. iMac is running el Capitan on the latest version of iTunes. My wife also uses the iMac on a separate account with a different iTunes account. The only thing I've done different recently is log onto my son's apple TV with my account so we could watch one of my films. Any ideas? Thanks in advance.