Can't add animation element?

Hi I am experiencing an issue where I am unable to add additional animation elements to my object. (The size parameter) I have been able to up to this point but now I cannot add additional elements.

What could be causing this? Thank you!

[16102-animation+size.jpg|16102]

Where it says ’ “Animation” idle ', is where you want to drag your new animations. Drag it right over idle and it’ll add it in.