Any research on WatchDogs model file format has been abandoned. The particular error indicates an unexpected (unknown to the moment of development) object type found in a hierarchy. Likely to be a non-bone extension like some specific physics bone, link or something I have not met in peds or vehicles I used to test.
I remind most of ped/player models were able to read (CHAR*** folders). And I've used just few vehicles in my test (muscle03 and one more).