How do I fix bad shadows / Moire Pattern effect?

My terrain is casting broken shadows. they look like a fishnet pattern or more precise like a moire pattern. What causes these moire patterns and how do I fix it?

Here is a screenshot of the terrible looking shadows:

http://www.uneatable.org/screen/2013-03-12_00-19-27.jpg

alt text

What I did so far:

I made a basic heighmap terrain with no texture

Then I added a directional lightsource

The quality settings are on max

screenshots:

Directional Light settings:

alt text

Quality Settings:

alt text

scroll down to the section on Bias

file:///Applications/Unity/Unity.app/Contents/Documentation/Documentation/Components/class-Light.html

does it help?

next,

file:///Applications/Unity/Unity.app/Contents/Documentation/Documentation/Manual/Shadows.html