The screenshot says something about a skinnode. I would say you have to go through all the objects and check which of them causes the problem. You could do that by changing one by one from none to rendernode. It is very likely that you have to adapt something if you just download a model and want to put that to dcs. For example texture names, animations, arguments and so on. I don't think that any of the models you can download or buy is prepared for DCS.