Why cant i build the scene?

So im having a problem here and i dont know how to solve it. I build my scene and everything seems to work just fine untill i try to simulate it, when i simulate it, it sais that there is 2000 objects that needs to be build. As you can imagine thise gives me so much lagg in the simulation that im not even able to move. Anyone got a clue why this isent working?


You need to build lighting.
Click the build button to do a full build or the small arrow by build and set your build options
You may also need to add a light mass volume if the scene is a little big.
The volume will need to encompass the whole visible even area

Hey man thanks for your anwser,
Although its not because i dont know how to build. But when i tell it to build it seems like it builds everything, but then when i simulate the game it gives me this message saying 2900 objects need rebuilt.
Im not sure what happens but it makes it impossible to move inside the game.
(this time i tried adding light mass volume)

Best Regards

Lightmass trying to allocate almost 14GB of memory which is probably higher than your PC have. Also log pointing out that some of the InstancedStaticMeshComponents (probably trees?) have too large lightmap. Either reduce lightmap resolution / number of mesh components or use dynamic lighting.