Really has no sense to use billboards with Octane, because this engine is mainly designed to use 3D Objects. Also, some feature as
fake shadows, are not supported. Anyway, if you need them please tell me. Well prepary a library of 2D materials for Octane. Only it's necessary to remove "Forest Material" and convert the base material, which a Standard type.
On the other side, i've done some tests converting materials from the free models, and i can reproduce the problem of your previous post (i though it was crashing in the conversion process, not after it). There is a workaround:
1) Turn off Geometry->Consolidate Materials.
2) Convert materials.
3) Turn on Consolidate Materials.
This problem is already fixed for the next beta update.