You mentioned tetras, are you trying to build mesh volume data from popcorn's mesh importer? or do you just want to sample the surface of the mesh?
Also, there's a gotcha with skinned meshes and attribute samplers in general (attribute samplers -> samplers that you can override per-instance in the game engine), which is that they can't be sampled at evolve (well, they can, but what will get sampled is the original sampler in the FX, not the one overriden in the engine, so you won't sample the proper skinned mesh)
This is a limitation that will go away eventually when we have time to implement it but currently we're stuck with that limitation.
Also, could you send us your .fbx on support _at_ popcornfx _dot_ com so we can take a look at it and make sure nothing's wrong.
Our example skinned meshes in the "ReleaseHighlights" package available from the project launcher were all exported from mixamo so there shouldn't be any problems there.