No puedo importar archivos nif

En la consola de Blender me aparece esto: Blender NIF scripts 2.5.2 (running on Blender 249, pyfi 2.1.3). Traceback (most recent call last):
File c:\apps\blender\.blender\scripts\bpymodules\nIf_co mmon, py, line 1209, i.

N gui_button_event.

Self, gui_exit().

File c:\apps\blender\.blender\scripts\bpymodules\nIf_co mmon, py, line 1558, i.

N gui_exit.

Self, call-back(**self, config).

File c:\apps\blender\.blender\scripts\import\import_nif , py, line 3742, in co.

Nfig_callback.

Importer = nifimport(**config).

File c:\apps\blender\.blender\scripts\import\import_nif , py, line 254, in __i.

Nit__.

If root in [c for c in b, skin_instance, skeleton_rot, children]:
Attributeerror: nonetype object has no attribute children.

Ayuda por favor.