I fixed the vertex problem by setting max influences below 4, but there still seems to be something wrong. For one, when I create my own joints, they don't seem to be recognized by the modelviewer, it says in the log that they don't exist. So I tried to copy the joints from the grunt. They recognize those, and everything seems to be fine, but the viewer still crashes! This is the log:
The polycount is high, I was gonna fix that later, but there isn't any problem viewing the model if I de-skin it, so I'm not sure what's wrong.