I'm having this issue too. I have installed the attachment but still having the problem in 2015. (the attachment fixed the problem in 2016 BUT my lighting doesn't work in 2016, different issue..) Some of my forest items do work; forest fir tree and grass clumps are not working but maple tree and rocks, for example, work fine. Also if I put the fir tree in a scene by itself it renders just fine but when put into my scene I get the same error as suppenhuhn reported. Do you have any ideas what might be the problem?