Tweening in IR

I was experimenting with the tweening tool...

I was trying to make a gradient tween across the screen. In the book I read they tweened text across the screen. When I tried to tween, making it look like the gradient was moving along a nav bar, it would not work. I then made a bar using the shape tool and was able to make that work.

Is there something about a rasterized layer vs one that is not that makes this command work?

What you have to do is make the gradient about twice as wide as the nav bar (assuming that it is traveling horizontally) in a separate document, then drag it into the document with the nav bar line it up and drag it all the way to the (let's say) left. Then make a new frame and drag the gradient all the way to the right. Then tween with "position" selected and choose the right number of frames.

That should do it.