Smoothing groups problem

Gruby11

Even though I have all the polygons under the same smoothing group it looks like this.

MoP

Looks like you have some unwelded vertices there. Select the offending faces, convert selection to vertices, do a Weld action on the selection.

Yozora

It could also be that those faces have some other material on them, so you can try re-applying another default material on it.

Mark Dygert

You could also have some long thin triangles that aren't much bigger than the edge. If what was suggested above doesn't work. Try clicking on a vert and moving it, it might reveal some bad geometry underneath.

Ryno

What Vig said. Move the verts to expose bad stuff.