Terrain not correctly connected to a terrainData object Unit

Unity Engine
1

I tried importing the island demo terrain in my own project using export/import package. Everything seems fine visually yet I get this error:

Terrain not correctly connected to a terrainData object
UnityEngine.Terrain:CullAllTerrains()

Any idea ?

2

Where did you download the island source?

3

I bet that if you check out the terrain data object it will be empty.
Sounds very familiar to me and happens when you try to move terrains through assets between projects, at least did so with me and Unity 2.1 …