message says my computer is not authorized to play certain music i've purchased

Hello there, hendjc.

It sounds like you're being prompted to authorize certain songs even though your computer is authorized for iTunes. The following Knowledge Base article offers up some great steps for troubleshooting:

If iTunes repeatedly prompts you to authorize your computer

Although all four categories are applicable, many users find this section the most helpful:

Authorize your purchases with the correct account name

The items you're trying to play might have been purchased using a different iTunes Store account. To determine which account was used to purchase an item, follow the steps below:

1. Select a purchased song in your library.
2. Mac: From the menu bar at the top of your computer screen, choose File > Get Info.
   Windows: Press Control and B on your keyboard to turn on the iTunes menu bar. From the menu bar, choose File > Get Info. Learn more about menus in iTunes for Windows.
3. Click the File tab. Make note of the Account Name that appears in the list. This is the account name (Apple ID) that you need to use when you authorize your computer to play this purchase.
   The Apple ID that appears is the one that you used when you purchased the item. The Apple ID you used to purchase the item doesn't change, even if you change your Apple ID.
4. Authorize your computer.

If you authorized the Apple ID that is shown in the Summary File tab, check your purchase history for that Apple ID. If your purchase history doesn't reflect the purchase of the items in your iTunes library, think about any other Apple ID you might have created, and authorize your computer for that Apple ID.

If you forgot the password to one of your accounts, recover it using Apple's password-recovery website.

Thanks for reaching out to Apple Support Communities.

Cheers.