I see that you're provided a message when trying to download a free application from the App Store on your iPhone. It's saying that your Apple ID is locked and you're wondering why. I'm happy to help.
If your Apple ID is locked or disabled -- This is sometimes caused when an incorrect password has been provided too many times. The remedy is to reset your password. If you've recently changed your password, continue to the next article.
What to do after you change your Apple ID or password -- This also happens after you've changed the password for your Apple ID and haven't reconnected to Apple services with your new password afterwards. If you've recently changed your password, review all of the Apple services listed in this article, then follow the steps provided for the services you use.