1) Be sure Max is closed.
2) Rename the file Octane3dsmax.dlr in the max plugins folder to any other name. For example zOctane3dsmax.dlr
3) Run Max and render.
This is a side effect of the main problem, because Octane is not properly calling the Forest interface. Just click Display->Update in Forest to rebuild.To see again the trees in the viewport I have to click "manual update" in the display planel. I see the tree preview in the viewport, I hit render....no trees rendered...as soon as I hit render the trees are deleted from the preview.