Strange that you cannot reproduce it. I'm using max 2014 with latest updates. Anyway I was able to fix the error. I remembered a piece of advice you gave me one time about merging scenes with forest objects. I created a new scene and a new forest object. I then deleted the forest object and merged all the geometry from the file with the rendering error except for the forest templates. Now it is fixed.
I don't understand why the error only happens on my system but I won't dwell on it. Thanks for taking a look at it!