Null endpoint transform in an OffMshLink

Hi I am using navmesh with automatic generated offMeshLink. However, after clearing the navMesh, I have been getting the error “Null endpoint transform in an OffMshLink”. I do not know whether it is a related problem but my agents fail to use offMeshlInks now as well. I hope that someone can share similar experience as Unity seems to be lacking information on this.

Ya I done it. But the problem persist. Anyway I solve the problem. I added a offMeshLink to a gamObject but did not assign any start or end pt. This cause the error message to appear when baking the navMesh.