Import Error When Copy Avatar From Other

Hey, I import "Ethan.fbx" to Blender and after export without doing anything in blender and import unity again. When select Humanoid > Copy From Other Avatar i get this Import Message:

 Copied Avatar Rig Configuration mis-match. Bone lenght in copied configuration does not match position in animation file:
 >> 'EthanLeftLeg' : position error = 3.271901 mm

Thank you.