It just came to me

I think I have figured it out. And I don't see how I could possibly be wrong this time. You can't have a vertex belong to more than 4 vertex groups. That's what causes the error. I think I need to add this information to my RCT3 Animation tutorial. I should be given a medal or something for figuring this out.

I will report back when I have configured the model properly to conform to this quirky rule.