I have downloaded the Iron Man 3 movie but it won't download Itunes extras

Close iTunes

In the Finder, open up your iTunes Media folder. If you have it in the default location it is under ~/Music/iTunes/iTunes Media

Inside iTunes Media, open up Downloads

You may see one or more "Iron Man3 iTunes Extras" (or similarly named) folders. These are partial downloads which did not complete. If your problem is like mine, iTunes kept trying to pick up where it left off and kept getting stuck with an error.

Delete all the Iron Man3 extras folders. If you have other downloads in progress or that were partial, you can delete those as well. This is just a temporary folder where iTunes stores the downloads until they are processed into your iTunes library. These downloads are also already registered to your iTunes account, so they are available to download if they are not in your library.

Open iTunes, it should check for downloads automatically and begin downloading your file.

If not, open the STORE menu (at the top of the screen) and select CHECK FOR AVAILABLE DOWNLOADS at the very bottom. This should begin downloading the iTunes Extras from the beginning.

Once I restarted from the beginning, Iron Man 3 iTunes Extras downloaded fine.