I have the same problem and I'm unable to download the trailers for 'Adjustment Bureau' and 'Never Let Me Go'. I keep getting error messages telling me the iTunes store is too busy. Come on iTunes, please sort it out.
And now movie trailers won't download at all - the 'free' button no longer exists, just the word free and clicking on that just starts the trailer playing but not downloading.
Seriously? Apple? This error has been going on over a MONTH with out any kind of attention? what gives? This error is Limiting the Trailers Publicity Publically, and I'm sure 20th Centry Fox would LOVE to know that iTunes has these un-addressed errors when people have been trying to download the "The Chronicles of Narnia: The Voyage of the Dawn Treader" trailer to put up in their movie cinemas preview screens! In fact, I do believe I may be sending one of those emails off myself!