"Assertion Failed: undefined must be a subclass or an instance of Ember.View, not " with no useful info

I started getting this error, but all attempts to debug the reason failed.

The whole info is like this:

Ember.assert    @   ember-1.10.0.debug.js:3940
readViewFactory @   ember-1.10.0.debug.js:39239
viewHelper  @   ember-1.10.0.debug.js:7521
inline  @   ember-1.10.0.debug.js:7948
render  @   VM4480:884
render  @   ember-1.10.0.debug.js:44625
EmberRenderer_createElement @   ember-1.10.0.debug.js:40279
Renderer_renderTree @   ember-1.10.0.debug.js:8768
ensureChildrenAreInDOM  @   ember-1.10.0.debug.js:41922
_ensureChildrenAreInDOM @   ember-1.10.0.debug.js:41885
invoke  @   ember-1.10.0.debug.js:854
flush   @   ember-1.10.0.debug.js:919
flush   @   ember-1.10.0.debug.js:724
end @   ember-1.10.0.debug.js:149
(anonymous) @   ember-1.10.0.debug.js:552

which doesn't help me at all. Nothing is pointing me to the element that is failing, and at the same time a lot of ember elements fail to render.

Any ideas what I'm doing wrong? Or how to find the exact problematic problem?

(Installed Ember inspector which also doesn't help me at all.)