Error normalizing vertex bone weights
This can be happening in only one case that you have some vertices without any binding. You need to check that in to look in the “obj directory” where you will see an XML file corresponding to each imported model.
This holds the geometry data in text file So, You need to examine and make it sure that every geometry content node does contain a weight channel and every entry has non zero data in that weights channel.
You can also get some more good information by visiting this website