Problem synching iTunes with iPhone

I just added some music to my iTunes library on my Macbook Pro and wanted to synch it to my iPhone. As I begin the synching process I get this message:

This computer is no longer authorized to play purchased items that are on the iPhone __'s IPhone”. Would you like to authorize this computer for items purchased from the iTunes Store?

I click AUTHORIZE and a box pops up with an ancient Apple id that I haven't used in many years. I replace the old id with my current one and get a message that I have already authorized three devices with this ID. I click OK and the above message pops up again.

Why is "this computer no longer authorized to play purchased items that are on my iPhone and how do I get out of this endless loop?

I subscribe to iTunes Match but have turned it off on my iPhone because I understand that must be done when synching to the iTunes library on my Macbook Pro.