I have been going through All my X Frogs and odd thing is the Palm type tree seems to be OK, but it is the Broadleaf and Pinus variety that do not work.
I concur with you about your source, those trees seems to work well and I have used some of the Broadleaf TIFF files on them and theye work just fine. Understand this. The Froggers I have were Free in dot MAX format. So I downloaded the 30 day free trial of 3DMax2009 and converted them to Wavefront Object. This worked very well in all my other landscape apps ie Vue and Terragen 2 and a friend tried them for me in Bryce and said they are great, but not so in Carrara and as I said above I am finding it is the Broadleaf and the Pinus, (Pines, Furs, Cypress etc.), that are giving me the problems. I will do a render in T2, Vue and Carrara of the White Fur and be back soon for a posting of the results.

I would rather be Politically Incorrect,
Then have Politically Correct-Incorrectness!!!