Transferring Animation to base-FBX - Deformed Animation

Hi all,

im struggeling with transfering an animation from one FBX file to another FBX. Both FBX share the exact same armature. The only difference is, that the one FBX stores an animation, which i want to transfer to the other. So, I set up everything accordingly, armature as generic, created an avatar, set up a animatorcontroller etc. .
But when i put the animation via animationcontroller on my base-FBX, the animation gets weirdly deforemed. I tried, using the humanoid rig, but the outcome was the same. At this point i double checked my armature of the base-FBX and animation-FBX but its the exact same. Bone orientation ist also the same. I really dont know why the mesh becomes deformed like that. Does somebody has any idea how to fix that, or what could be the problem? Modelling, Rigging& Animation were done in Blender.

The first picture shows the base-FBX. The second, the animation i want to give the base-FBX. The lowest shows the outcome - the deformed animation.