How can a rigged model be used multiple times in a scene? I've created a rigged model and created and grouped the model and rig. 

I would like to add it multiple times in a single scene. I used File > Append selected the group, made it local L and created a proxy Ctrl + Alt + P. 

But I can do this only once, when I try to repeat the procedure described before nothing happens. 

It works when I save the group in another file, and link two different groups into the scene. 

What am I doing wrong?
One you have imported the model. You can add it to the scene just as you would add any other object. Just open the Space Menu and go to Group Instance and you should see a new entry there for the rigged model.