I used the Animation and Rigging Toolkit to create and rig a skeleton with the basic Mannequin skinned to it, I then used the Toolkit to make a couple of animation cycles which I exported to FBX with the ‘Export Motion’ tool.
However trying to import this FBX to UE4 as a skeletal mesh doesn’t work.
This is the error message:
note that ‘Import as Rigid Mesh’ is actually enabled, it makes no difference to the import or the error message
I had this exact problem because I had not skinned my bones to my mesh. I also had to disable rigid bones/mesh in the import dialogue and enable the mesh bones option.