It's possible you may have deleted a bit more than you needed too. An easier way to get rid of an unwanted material would be to either A - edit the CR2 or B - edit the OBJ in UVMapper so that no group uses the material and then save a new obj from that.

Without looking at the files, it'll be hard to tell where exactly things went wrong but I've a feeling something got deleted that shouldn't have if the other shirts show up fine (despite having an extra material) and this one (without the extra material) is showing up flawed.