How do you fix them

Go in manually to whatever program you use to model, and reassign smoothing groups. IE In 3d Studio Max, you would go under the Edit Mesh modifier, select the faces (face or polygon tool) which you would like to smooth together, then at the bottom of the edit mesh modifier window, select the group number which you would like to apply to those faces.

Bear in mind if your using the MaxScript SMD importer for Max to import and SMD it will destroy all the vertex assignments in the skin modifier.

when i have them in ms3d i just open my
model in lith unwrap and resave the model
that normaly fix it ..
i don't know what lith unwrap has that ms3d
don't have ..

LithUnWrap actually destroys the smoothing groups and assigns everything to one group. After you save out with LithUnWrap if you had faces with different groups you have to re-do them.

So lets say I'm using MS3D, because I am. How do I go about fixing smoothing errors, or will the import export trick work? I Havent tried it yet

The path I use for Milkshape is:

Model in MS3D -> UVMap in LithUnwrap -> Set smoothing/vertex assignments in MS3D -> Export Compile.

LithUnWrap has a habit of breaking bone/vertex assignments and smoothing groups so its pointless doing it until the UV mapping is done.

One thing I've noticed is not many people actualy *bother* using smoothing in models, or at least not properly. They tend to assign everything to one group which makes faces that join at acute angles look awful.

If you look at one of my models, say the v2 of the Brit Airborne, you'll where things like the soles off the boots are smoothed seperately or the eyes aren't smoothed as part of the head.

Good smoothing is important to help the graphic card correctly shade and light surfaces.