Now, at first this kind of made me regret going back to the lower poly mesh, since it wasn't the complexity that was the problem. However, it was so incredibly frustrating to weight paint the hi-res version that I think it is worth going back to the low-res version just to make the weight painting easier.
Back to our timeline: Yesterday all I did was try and figure out what the importer doesn't like about the model. The only thing I concluded was that since it can't be the size, it must have something to do with the vertex groups/weight painting. However, the Warrior of Light model uses vertex groups to define weights for the various vertices, just like this model. And there are no problems with it. I figure I just have to keep looking and I will find some strange thing that I did that causes the error. That's the nice thing about Blender. It's always something you've done. It may be frustrating, but you can always correct it. However, what's really frustrating is when a program malfunctions, and you have done nothing wrong. Then it's almost impossible to get it working right.
I'm looking at you CryEngine 2.