Shading error on object

I got a small scenery with 3 buildings (a tower, a wall and a gate) and on 2 of the objects are shading errors. (1 on the gate and more on the tower. The wall is perfect.)

If I put a lightsource that is not ambient I can see some triangels on the objects. In form of a triangle a small part of the (flat) wall is getting a different (a darker) shading, than the sorroundings trianlgles.

I heard it can be a problem with different smoothing groups.
I used 3D Max to make the obnjects and in Max is no error to see, the objects can be rendered well, only after exported as 3DS and loaded in BLitz3D I see these ugly shading differences. I have looked on the smoothing groups in Max but was not able to find any error and I was not able to change it.
Any idea what I could do? Anyone made the same experience ?

Try exporting using b3dpipeline instead.

Make sure that all vertex pairs close to each other are welded. I get this problem with Milkshape, and its a pain to check every vertex on the model, but it has to be done.

it could be that you have edges that need turning or that some of your walls are not planar.

I could be wrong here but also if exporting using 3ds, vertices have a habit of becoming unwelded for some reason.