[solved] Linking objects

So I am playing around with an animation file. I linked in a object to animation, then I deleted it because i made a mistake. I went to link it back in and couldn’t/can’t. I know how to link objects. If I open a blank scene I can do it. I can also link another object no problem. Once I link it in once and delete I can never link it in again. What am I doing wrong?

Attached file:
Ball Bouncing complex.blend (526 KB)