Shadow Issue

Hey there I modeled this folder in maya and also generete the UVs in there. But I get this shadowing error on my mesh. I use a light map resoultion of 128.

Add a lightmass importance volume and rebuild your light.

Also take a look at this site:

Did I have to set up somethin when I placed the lightmass importance volume or just place it in the level scale it over the area and rebuild light ?

Just palce and scale it -> the lightmass importance volume is here to specify an area which should get a better light result