Q: I run iTunes on my iMac and keep my library on my external HD. When I go on vacation with my MacBook I am unable to play the music from my iPod via iTunes on my MacBook because it’s not authorized. I’ve never done this before, can someone please advise?
A: The likely problem here is that your MacBook is not authorized for the iTunes Store account that was used to purchase your music. Since you likely purchased most of your music on the iMac and synced your iPod from there, this computer would have automatically been authorized, but your MacBook will not be unless you have actually purchased content on it or you have authorized it manually. Although your iPod can play the music since it was authorized by your iMac, the MacBook itself also requires its own separate authorization.
Since Apple permits you to have up to five authorized computers, the solution to the problem is relatively simple: Choose Store, Authorize Computer from the iTunes menu on your MacBook, and enter your iTunes Store user name and password when prompted.
This will download the necessary authorization information from the iTunes Store so that your computer can play any content purchased with your iTunes Store account. Note that if you have more than one iTunes account that you have purchased content from, you will need to repeat this process for each account.
Note also that since you’re limited to five authorized computers, you should also ensure that you DE-authorize your iMac or MacBook should you ever sell them or take them in for service. This is accomplished by choosing Store, Deauthorize Computer from the iTunes menu.