I've found a mistake in the example script CameraImageAccess for getting the camera texture.
There is a problem when calling:
The problem is that, in the example script, the Texture2D has not been created.
I've fixed this by adding this line at the end of the Start method:
texture = new Texture2D(Screen.width, Screen.height);
However, although the error is gone, I still cannot see the camera texture (I apply it to a material with the following line):
meshRenderer.materials.mainTexture = texture; // meshRenderer.materials assigned from the inspector