The API has changed a bit since recent versions. There is now two separates command to append (bpy.ops.wm.append()) or link (bpy.ops.wm.link()) datablocks. bpy.ops.wm.link_append() is not valid anymore.
To append an object, you can use something like: bpy.ops.wm.append(directory="//your_directory//your_file.blend/Object/", filepath=“your_file.blend”, filename=“your_object”)
I’m working with Blender 2.69 and I can’t use bpy.ops.wm.append():
File "/usr/share/blender/scripts/modules/bpy/ops.py", line 188, in __call__
ret = op_call(self.idname_py(), None, kw)
AttributeError: Calling operator "bpy.ops.wm.append" error, could not be found
When I use bpy.ops.wm.link_append() with the same parameters: