Is it perhaps a pathway problem? I tried to find the specific pathway to NewMotionTree but had no success.
Well, I tried to create Ania with the AT rifle and worked just fine. My ania.abp file looks like this:
--3DSMax Toolset Generated: abp_functions.ms--
model =
{
"..\\..\\..\\common\\NewMotionTree.abp",
"..\\..\\..\\common\\base\\femalemotion\\femalemotion.abp",
"..\\..\\weapons\\rifle_mosin_nagant_sniper\\rifle_mosin_nagant_sniper.abp",
"..\\..\\props\\demolitions\\demolitions",
"..\\..\\..\\british\\weapons\\boys_at_rifle\\boys_at_rifle",
"ania",
}