Lighting wont build

Hello, I have a problem with building my lighting in my scene.

1st, I cant get rid of the black grid lines from my landscape, even after I rebuild my lighting, look at the image below
Imgur
2nd, after I finish bulidling my lighting and go in to play mode, an error appears on the screen - LIGHTING NEEDS TO BE REBUILD(409 unbuild objects) like in this image - 2 | Iskren Ivanov | Flickr

Hello jugarnaittt,

I would like to gather some more information from you in order to narrow down what is causing these issues.

1.) Can you link me a copy of your DxDiag?
2.) Does this happen in a “New” blank project in 4.9?
3.) If you set all of your lights to dynamic does this still happen?
4.) Make a copy of your project before trying this troubleshoot If you delete your folders in your projects root folder labeled “Intermediate, Saved, and Derived Data Cache,” and keep your lights static, can you build lighting then.

Logan