I tried to purchase a movie using the iTunes Store on my iPad, but the purchase was declined due to insufficient storage. Why?

I have the Sony Movie Of the Day app. Each day it highlights a new movie on sale at a significant discount in the iTunes Store. Today I went to purchase a movie from iTunes using my iPad but the purchase was declined due to insufficient storage. Why should the storage on my iPad affect what I can and cannot purchase from the iTunes Store on my iPad. I am out of town and by the time I get home to my PC and my iTunes the movie will no longer be on sale. Other than deleted stuff I don't want to what can I do?