I can’t be specific with the problem, but I suspect it stems from Carrara being designed to use bones for 3D instead of 2d. And, if the mesh density isn’t high enough, Carrara may simply not know what to do. If it’s going to work, each vertex plane will probably need to have about 500 polygons in quads with no triangles - triangles and bones do not play well together.

Programs like Moho (anime studio pro) and other 2d animation solutions are designed specifically to handle this stuff. If your budget allows, and if Carrara can’t deliver on the 2d bone rigging, you might want to check out Moho. It’s very powerful and easy to use.