Problem opening .nif's

Hello. I would like to open .nif’s in Blender so I could make small changes to units in the excellent game Civilization IV as I am currently working on an own scenario for that game.

However, Blender doesn’t want me to. I get an irritating error-message when tryig to import .nif’s into it (Blender NIF Scripts 2.4.10 (running on Blender 249, PyFFI 2.1.2).; Attribute Error ‘NiTriStrips’ has no Attribute ‘isSkin’). Can anyone tell me what the problem is and what I need to do to solve it?