I also ran into this error while creating static meshes in code, and found another possible cause.
It looks like you see this error if the winding order of a triangle is inconsistent with the vertex normal. i.e. If the winding order of that triangle suggests a triangle (face normal) facing in one direction but the vertex normal is pointing in the opposite direction.
My assumption is that there is a dot product involved in calculating the tangent vector that is being clamped in the range [0…1] which is resulting in a zero length tangent, which is what I was seeing. Not that it really matters why.
In my case I fixed this by correcting the winding order of my triangles but if you are coming from a modeling tool I guess it could be caused by a rogue normal pointing in the wrong direction.