One possible reason for this is that itunes may need to be updated.If itunes isn't letting you update because the version of yourcomputer software isn't recent enough, try goi
…ng to apple.com todownload a slightly older version of itunes than the one you aretrying to download. For example; If you are currently operating onitunes 8.1, and the update is for itunes 10.1 but it won't let youupdate, go to apple.com and locate old software to download (thisshould be free!) and download itunes 9.2. This worked for me, sincethe itunes store had a new format and was no longer compatible withthe old version... to avoid further problems, I know now to alwaysupdate as soon as new updates are available! (MORE)