So I created a barrel in 3ds Max and imported it into UE4. I made a separate UV channel with no overlapping UV’s, but when I build the lighting it says it has overlapping UV’s! This is the only object that is giving me problems. I attached an image of my lightmapped UV’s for the barrel… nothing seems to be overlapping, so what’s the problem?
Thanks !
In UE4 open the static mesh and make sure that it is set to use the correct channel for your lightmap UV’s
Also, if you do your UV’s by hand you would get better lighting results, like on a barrel you could have a seam around the top and the bottom and then just put a seam straight down the side and it would then only have 3 UV islands and the lightmaps would look much better.
Hey Majkl! 
Maybe one of your UVs is folded onto itself, or maybe you forgot to set the lightmap index.
Though the bigger issue here is how many shells you have in your lightmap. The goal is to have as little amount of seams, and as few amount of shells as possible. If this is a barrel I assume it is 1, 2 or 3pieces, right? If so than that is how many shells you should have in your lightmap. If this object was working and you baked lighting to it there would be so many dark seams it would be unusable. Unless you cranked the resolution way to high.
Check out this doc that goes further in depth into creating proper lightmaps. (Your issue is towards the bottom, But I would suggest reading the whole thing.)
Hope that helps!
Once i made object that contained 3 uv channels i used first for textures second for light-maps and third for some additional details. There was no overlapping parts in second channel however i still received warning because of third channel with overlapping islands