iTunes: Missing folder or incorrect permissions may prevent authorization

With Mac OS X, the Shared folder is required to authorize your iTunes Store purchases. With Windows the iTunes folder is also required. If either of these folders are missing or have incorrect folder permissions, you may notice one of the following symptoms: You are unable to complete a purchase from the iTunes Store. You cannot play content you purchased from the iTunes Store. An alert appears with the following text:"There was an error storing your authorization information on this computer. The required directory was not found or has a permission error."