Problem porting to source

Ok so currently am trying to port this paramedic bag model and a few other models but I keep getting this error when I try to export it, could anyone try enlightening me as to why it’s throwing this error? I’m doing the exact same thing I did with models I ported earlier but with different models/textures of course and yet now it causes this issue

http://puu.sh/jCWmj/5ff3dfa740.png

If you’re planning on having the armature with the model, you will need to merge the armature with the paramedicbag mesh. You can do that with CTRL + J. I’m no expert but it might work.

There is no mesh data to join it says and I’ve never had to join them before