failed: the filename, directory name or volume lable syntax is incorrect

a friend and i are working between mac and pc... bouncing file exports back and forth up until lately i have received an error when importing that makes me either retry or force close unity. what could this error mean? does it mean that my partner has accidentally changed something within a file name that is confusing the path to certain items in the scene? basically the file will load after force quitting... the new file that imported is missing the character models, their controllers and animator configurations. aside from these, missing textures and various other missing things i have seen in his builds of the same project. any help would be greatly appreciated! thanks guys... this is destroying our work flow.