Music from different library to iphone

I used to be able to add stuff from other computers to my iPod or iPhone by tucking manually manage in the settings. I updated iTunes lately and now I can't seem to add music manually from the computer I use to download stuff. Does anybody know have apple stopped this being allowed or am I doing something wrong?

When I try to drag the music across the symbol changes from the number of items I'm trying to drag to a red circle with a line through it.

Anybody help me on this one I really want to listen to new arctic monkeys and queens of the Stone Age albums!!!