"Invalid clnors in this fan" warning I have this jointed arm model in this blender file.


First of all I am joining "left_arm" and "left_arm_ring_in_part" with ctrl+j after selecting both of them.

After that, I am selecting my new joined object "left_arm" ,switching edit mode and click on "remove doubles" button it gives "Invalid clnors in this fan!" warning twice after removing doubles. It doesn't seem problematic now but sometimes it gives that error almost 200 times repeatedly (e.g. while using "3D add-on" on this left arm for make manifold operation). 

Does anybody know how to solve that ? Thnks in advance.
The problem is due to custom normals. "clnors" means "Custom Loops Normals".

The meshes have custom normals which means that their normals have been set (instead of auto calculated). When you join several meshes and/or remove doubles this custom setup cannot be maintained.

On each mesh you should do the following (before of after joining them):


Use the "clear custom normals" button (in the geometry data panel)
Remove doubles
Set smooth
Uncheck 'auto smooth'