Terrain Tree Painter keeps crashing Unity

I am following the the terrain tutorial in the Unity Game Development Essentials. Great book for beginners btw. However when I attempt to paint the trees it crashes. It allows me to set the values in the Inspector, and load the mesh. As soon as I click the terrain to paint. Crash.

This is what I am setting my values to:
Bend Factor:0
Brush Size:10
Tree Density:0
Color Variation:0
Tree Height:35
Variation:10
Tree Width:35
Variation:10

Here is the directions from the book(It is for an older version of Unity, but I adjusted values for my 2.6v):

Bend Factor here allows our trees to sway in the wind. This effect is computationally expensive, so we'll simply use a low number. Type in a value of 2 and press Enter to confirm. If you find that this is causing low performance later in development, then you can always return to this setting and set it back to zero. Click on the Add button to finish. With your palm tree in the palette, you should see a small preview of the tree with a blue background to show that it is selected as the tree to place. Set the Brush Size to 15 (painting 15 trees at a time) and the Tree Density to 0 (giving us a wide spread of trees). Set Color Variation to 0.4 to give us a varied set of trees and Tree Height / Width to 1.5 with their Variation settings to 0.3. Using single-clicks, place trees around the coast of the island, near the sandy areas that you would expect to see them. Then to complement the island's terrain, place a few more palm trees at random locations inland.

I am loving this engine so far, and this is the only hiccup I have had. Any ideas from the experts?