Switching skybox in gm_construct, but failed remarkably

So lately I’ve been attempting to change the skybox in gm_construct to a dark and eerie skybox (sky_borealis01), but all it did was make the map lighting glitch the hell out. I can see the corona of sunlight that shouldnt be there, the skybox is showing a huge cascade of multiple pictures of what the skybox should be, I can see through the roof of the little room, everything is just generally messed.

Could anyone help me out and do a step-by-step thing on how to do this?

Try the mapping section.