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

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