Animated Gif Drawer error in build

Hi, thanks for your time if you're reading this. I'm using the Animated Gif Drawer (http://wiki.unity3d.com/index.php/AnimatedGifDrawer) script to play some gifs throughout the game. It works in the editor, but when I make a built I get this errors:

TypeLoadException: Could not load type 'System.IO.InternalBufferOverflowException' from assembly 'System.Drawing'

I've followed instructions and copied the System.Drawing.dll to the Assets folder, but it somehow doesn't work in the build.

I'd be grateful for some help.