If you cook something as a triangle mesh then you have to load it again as a triangle mesh. If you cook something as a convex mesh then you have to load it as a convex mesh.
Triangle meshes and convex meshes are not the same binary files, even though I use the same filename extension (.nxb) for both in my samples. You can use different extensions if this helps you keeping your models organized.
Please note that triangle meshes are for static geometry (things that never move), and convex meshes are for dynamic geometry (things that move around in the scene).
enn0x