Why Doesn't Submission Like .obj Files?

[DogToon64]

One thing I would suggest is by exporting the model you're wanting to export through Model > Export selected objects (split).
It should export the model as an .fbx file. (It's very similar to a .dae file, except it's not as widely used as a .dae file.)

From there, you can export the .fbx file as an .obj file (with a .mlt file) in Blender.

Hope this helps!