Strange problem with model editor

[Your Computer]

But the material file is in the same directory :/ Still doesn't work >.<

Maybe the .mat file needs the same file name as the model (i.e. without the .dae extension, of course), or maybe the image format you're using for your texture(s) is unsupported. It may also be possible that you used multiple textures for the same one mesh (IIRC, only one texture per mesh is supported). This, assuming you didn't pick "decal" for the material type.