Terrain Heightmap Can't Attach

Hi I am trying to attach a height map to a terrain. I’m getting the error Argument Exception: Destination array is not long enough to copy all the items in the collection. Other people have asked this question and got no replies. Can anyone please answer this?

Terrain Heightmap pixels are stored in a 2 Dimensional Array, maybe that array is not long enought to store it start looking in this direction also check documentation in terraindata so you can see what data is stored in arrays