"This computer is already associated with an Apple id."

I purchased music via iTunes on my iPhone 5s. I signed into itunes on my mac mini and am trying to download my "purchased" music onto my computer. I am clearly signed in because I can see my user name at the top left of the itunes store application. I can view all the music I purchased, yet when I click on it to download this message pops up "This computer is already associated with an Apple id." Here is what I have tried to no avail.

-I authorized my computer (even though it has already been authorized when I bought my ipod/cell phone years ago)

-I deauthorized my computer, then reauthorized my computer. Did not fix my problem.

-I made sure I was running the latest OS as well as the latest version of iTunes. Which I am.

-I went into my username>account> to the page Apple ID summary to read my "Computer Authorizations" to which it said "One computer is authorized to play content purchased with this apple id." Which is obviously this computer.

-I went further down on the Account Information page under iTunes in the Cloud to which is said "Manage Devices: 1 device is associated with this Apple ID and can download your purchases from iTunes in the Cloud.

So I obviously do not have too many accounts associated with my ID. I have the current version. And I cannot get music I purchased on my iPhone onto my computer.

ALSO: IF I am getting this message, then what Apple id does iTunes THINK my computer is associated with???? I've always used this one!