Everytime. It displays the following message below.
keep in mind i’m running a i7 with 16 GB Ram and a 4GB memory Graphics Card.
What in the world is going on here ppl?
Not enough RAM. Try increasing the amount of virtual memory on your system, that may help.
^ i have 16 GB of them?!?!?
Yes, but that map is huge and Epic built it with larger memory systems. Anyone else excited with 4.5 Update? - Cinematics & Media - Epic Developer Community Forums
Processes like that tend to be memory hungry, just try running swarm with task manager open and you’ll see whether was right.
I’ll be damned
If you are building something based on the landscape demo, you should use dynamic lighting instead (or until the ram usage is fixed by Epic).
All you need to do is find the directional light in the level, and change it from Stationary to Movable. Then open up the world settings and under “Lightmass”, check “Force No Precomputed Lighting”. One last thing to finalize it is to do one final build of the lighting, and you now have Dynamic only lighting, and won’t need to build lighting ever again!
If you need to go back to lightmass in the future, just follow these steps backwards. 
The platformer demo is doing the same thing when trying to build with DFAO on. It says array index out of bounds instead though…
I havent downloaded it yet but why do you have DFAO enabled if you are building the lights?
i deleted all the lights except the directional light and skylight.
EDIT: or you mean why use DFAO if im not using LPV?
Yeah, DFAO is aimed for dynamic lighting and it isn’t perfect yet so that may cause some problems. Was it enabled for platformer game by default?
negative. i enabled it. personally i like DFAO even though its inefficient and a work in progress right now.
4.5 has an improvement to Lightmass’s memory usage. With that change the LandscapeMountains demo builds in 10.5Gb, instead of the previous 19Gb.