On itunes, I can freely download content onto my IPOD from any computer (provided obviously i only have up to 5 activations at a time). But I'm having trouble with my iphone

But I am trying to download a tv show Ive just downloaded onto itunes on a mate's computer and its not letting me! It detects the iphone fine, but it doesn't let me drag the show onto my iphone icon. It's the same with music. Any help? Is this an irritating iphone only issue? Any resolution?