iBooks preorder won't download

I know this issue has come up before, but, back in September, I pre-ordered a book that came out yesterday. When I open iBooks or go to the Books tab in iTunes the button is greyed out and says 'Purchased', but it has not been downloaded, and doesn't give me a way to do so. I have quit the apps, restarted devices, still there is no progress. It is infuriating. Has anyone ever solved this problem?