Asset store import location

I am attempting to use NGUI, specifically I was trying to script a image button's normalSprite, hoverSprite, and pressedSprite.

The following command was failing.

muteButton.GetComponent(UIImageButton).normalSprite = "speaker_off_white";

I believe I found the answer (though I lost the URL). I believe it has to do with the fact that assets are compiled in a specific order. As such, I tried to put my imported packages in a "plugins" directory. After doing so, the above command started working. Now, however, quite a few of the scripts and components (including "Transform") are displaying the message:

Multi-object editing not supported.

I'm baffled why this happened, but I assume it has something to do with moving my assets around. Any guidance?