Why Doesn't Submission Like .obj Files?

[hopper13]

Hello everyone, this is my first post to the VG resource!

Just yesterday I installed AssetStudio, and just this morning, Blender. (Yes, I still barely have any idea what I'm doing). Anywho, I tried to submit a model of a character from the game Club Penguin Island (a ZIP with two files, completely unaltered from the game- Rookie.png and rookie_mesh.obj) to which I saw this message upon checking my pending submissions:

This submission has been flagged for the following potential issue:

• Contains at least one .obj and .mtl count is less than .obj count
  

Can anyone please explain what this means, why it's an issue, and what I can do to change it? Thank you!

(Reposted from General Ripping)