Having trouble deauthorizing a computer.

I'm having trouble de-authorizing a Macintosh.

It works perfectly, and would like to continue to use it, but we are at our limit.

First, let me say I'm reasonably confident, (but not absolutely confident) that this computer was authorized. In fact, to get to the section where the ID is de-authorized I had to sign in with my Apple ID.

I did the following:

1.) Open iTunes on the computer you want to deauthorize.

2.) Choose Store > Deauthorize This Computer.

After doing this, I received the following pop-up. " This computer was not authorized. To authorize this computer, play a song or video you have purchased using this Apple ID."

This message leads me to believe the computer was never authorized to begin with. I am confused.