[idas]

Only this one window ?

I mean that your scene have something (material or surface) which is not supported by Maxwell.

Check your scene, or try File > Optimize Scene Size...

[idas]

I had this problem, but i dont remember.

Now you can try select all objects from persp. camera view and File > Export Selection. Then open exported scene, create new Maxwell camera and re-render...

[Witt3D]

The usual problem when this alert apears, is a problem with the triangulation of tha polygons.

Any type of error while is trying to export the meshes to the maxwell scene, cause this type of error.

Try to select each polygon and to try again the render process. So until you find the troublesheet polygon.