I've made simple model (mesh and bones) with bones in blender, and exported it in fbx. Vertexes were tied to bones in blender. Then imported fbx in MED. Saved mdl, then rotate model as I need it, center it and scale 10 times, cause usefull model size varies in blender and in MED (without scale model will be too small).
Then I created simple bones walking animaton (4 frames). And when I played this animation in MED it's looking quite good. But when I played it in Engine Preview - all its moving parts was messed, it was like moving cubes (no interpolation) on bones. See image
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Then I converted bones animation to vertex in MED, saved it in run preview again. And ... it looks normal as it should be -

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What is wrong? Can anyone give me the way to fix my bones animation, cause I want to add bones animation to my char (only one vertex animation can be played in moment, but you can play 2 or more bones animations simultaneously).

I think your problem comes from the scaling part.
You have to figure out what size to make your model initially in the 3D modeling program of your choice so that when you import it, no scaling is required. It's the scaling of the bones that makes it go all wonky if I'm not mistaken. My wife's a pro animator for EA. She was just talking about this the other day. If that doesn't help, I can try and get some more specifics.
She also mentioned just baking all the animation and export it all as vertex animation, since that's what the engine seems to prefer. But if you want more than one, you have to deal with additive blending.

At last i found the problem - it was my bad, begginers mistake, i was moving bones instead of rotating them
Now it goes well.