@Erikari @Harald, thanks for the input.
The programmer finally found the solution, it was the CAPS on the file name and the main root bone. You see, I was working on two project, one was using unity and already established to use CAPS on file names and root bone names, the other was using cocos 2d, and was using small letters for file names and root bones. I don't know that these things can really affect the material loading. I got mixed up in the middle.