"BIOmatic" rendering troubles with AO

I rendered an interior scene with Blender’s native renderer’s Ambient Occlusion and have any unexpected troubles.

http://s0.imgsrc.ru/q/qmdx/4/15489954oei.jpg http://s0.imgsrc.ru/q/qmdx/0/15490470sJm.jpg

Green grass suddenly became purple and I had to inv its texture.
Here are the AO settings:

Have any ideas about it?

As far as the washed out colors are concerned:
In Shading (F5) -> World Buttons -> World, set the Ambient RGB value to black.

My guess is that the combination of Sky Color and Both are what’s doing it. Try setting the AO to Add. I’ve never needed any other than Add mode, and gotten unreliable results from Both. I’ve never found it useful for lighting a believable situation.

Thank you.
I will change my settings.

I made changes to the settings AO