Terrain Toolkit with Unity 4

HI I am trying to install the terrain toolkit, I download, unzip and drop it into unity as the instructions say, but i got the error:

Assets/TerrainToolkit/Editor/TerrainToolkitEditor.cs(40,68): error CS0117: Resources' does not contain a definition for LoadAssetAtPath’

Please help, so i could use it

http://www.unity3dbrasil.com.br/packages/index.php/component/content/?view=featured&start=138

Go to the terrain article