Why is rigging with automatic weights failing?

I dont get why rigging with automatic weights is failing in both blender and mixamo. Can someone look at my model real quick and tell me whats wrong? ( please tell me that i textured it wrong or anything thats not related to this very problem. It was a test nothing more )
.blend is in the description. Im having problems with the model named knight.

Thanks in advance!

ATTACHMENT:ritter.blend (2.31 MB)

First off your scale is negative for the mesh in one axis, you can do Apply Object Transform (search with spacebar) and check scale to fix that.

If you do Select Non Manifold you can see that you’ve got a bunch of strange stuff like wire edges and n-gons. However as a quick workaround you can add a subdivision surface modifier to the mesh and then parent it and it will work. Why? Who knows, but it does and you can remove the subdivision surface modifier after that if you don’t want it.

An armor type of mesh with automatic weights won’t look that good though because armor doesn’t really deform, so maybe it’s better to just weight the parts of the armor to the bones that should make them move directly.

Jeah ill think about the last part. I dont really get the 2nd thing you mentioned. Please explain? Im not a native english speaker ;/
I just dont understand the part where you say “just add a subdivision suface modifier and then parent it” Parent it to what??

I meant parenting the mesh to the armature by clicking the mesh, shift clicking the armature and pressing ctrl+p and choosing with automatic weights, I guess it wasn’t clear. But with the subd modifier it should work.

I actually had a subdiv modifier on the mesh i just applyd it before rigging. Also its a bge mesh so applying another subdiv modifier isnt too good. Are you shure this will work? Have you already tried? Why doesnt it work with the first subdiv modifier? Because i applyed it or because i used decimate afterwards?

It didn’t work because you applied the modifier.

Yes, you don’t need to apply it, just have it as a modifier when parenting with automatic weights, that will fix the errors in your mesh (temporarily for the automatic weight to work), if you don’t want it after that you can just remove the modifier and the automatic weights will still be there.