Doofenshmirtz Project Revived

If you remember a few months ago, I said I was planning to mod Heinz Doofenshmirtz from Phineas and Ferb into Mario Kart Wii. However, I stopped short and abandoned the project. Now, a few months later and I have a bit more knowledge of modeling and stuff, so I tried to revive this project. However, I've run into a problem. When trying to import the Doofenshmirtz model (https://www.models-resource.com/playstation_vita/phineasandferbdayofdoofenshmirtz/model/29052/) through BrawlBox, it came up with an error, stating that "one or more vertices may not be weighted correctly." I know literally nothing about "weighting vertices," so could anyone with MKWii modding knowledge please help me out on this one?