I'm a newbie on NGUI also but I already got tweens (in your case animations) working on my panels when I click on buttons.
Simply:
-Attach UIButtonPlayAnimation to your button
-Fill in the parameters for it right in the inspector. No need to script anything for this.
-Check this example that comes along NGUI, there you'll find what you are looking for:
http://www.tasharen.com/ngui/example8.htmlIn any case, in your script I can see some strange things:
- OnLoadClicked() is not part of the NGUI events as far as I can see. It should be OnClick()
- UIButtonPlayAnimation is a class, you just can't use it like if it is a method...
Stilghar