I installed iOS 5, and now I can't download my purchased music or books (reader mail)June writes: Finally got iOS 5 on my iPhone after hours of trying, but now there’s a new problem. When I go to the iTunes store, it says I don’t have any purchased music to download, even though I’ve bought all kinds of music on iTunes. And my apps and iBooks app are acting strange, too. This is the worst ever, Apple!

Hi June, I feel your pain. I spent a good six hours trying to get iOS 5 installed on my iPhone 4 and iPad 2—and even once that was done, the iTunes app on both my iPhone and iPad kept telling me that I couldn’t re-download any of the songs I’d previously bought on iTunes (usually, you open the iTunes app, then tap the Purchased tab at the bottom), nor could I turn on automatic downloads (a feature that automatically downloads any new media purchases) for iBooks.

After a little investigation, I found the problem: my Apple ID—or rather, my two Apple IDs.

Here’s a question for you, June: do you subscribe to MobileMe, the old Apple online sharing service that’s now being replaced with iCloud?

I bet you are, and I am too—and that means we both have MobileMe user names, which Apple now calls an Apple ID. What’s your Apple ID for? Identifying you on the new iCloud service, for starters, as well as managing all your purchases on iTunes.

But here’s the thing: MobileMe users like you and me may well have a second, older Apple Store account that we use for all things iTunes.

How can you tell? Open iTunes, click the iTunes Store tab in the left-hand column, and look in the top-right corner of the screen, right below the Search box. If there’s an email address or user name listed there—and yes, it’s probably different than your MobileMe user name—click it to access the account you’re using for iTunes.

So basically, what’s happening here is that you have two Apple IDs—either because you’re a MobileMe user, or because somehow over the years, you just ended up with a pair of Apple IDs.

And no, you can’t just merge two Apple IDs into one.

Confused yet? Me too.

Anyway, here’s the good news: on your iPhone, iPad, or iPod Touch, you can use one Apple ID for iCloud, and another for your iTunes purchases.

Just go to your iDevice, tap Settings, Store, and find the Apple ID user name listed at the bottom of the screen. If it’s different than the user name listed on your iTunes desktop software, then click it, tap “Sign Out,” and then enter your old iTunes store login information.

Presto—you should see all your old purchases on your handset, ready for re-downloading (or at least, it worked for me).

Still having iOS 5 installation problems? Post ’em below.