Importing FBX failed to produce Skeletal Mesh asset, claiming its skeleton is invalid.

Hello, and please I need help.

When I import an FBX from Blender, it produces no Skeletal Mesh asset, but others are fine and I can preview the animations. (The material is created by me.)

It gave me an error log like this.

Previously I imported similar assets and they were fine. I have no idea why this is the case for this certain FBX.