Read this article on how to fix apps that won't update.
Thanks for the link, but the problem is not just with one app... It's pushing the "update all" button. The button turns grey and it just sits there and does nothing for about 10-15 minutes when it finally gives you the option of entering your password... Then everything works fine. This has only started happening recently and happens with both my phone and iPad.
Had the same problem. Apparently I reached my capacity and had to delete a movie. Updated without a hitch after I did that. Hope this helps.