After I build the lighting it starts encoding textures. Next I get this message
The asset ‘/Game/SimpleDungeons/Maps/Demo_Scene_BuiltData’ (Demo_Scene_BuiltData.uasset) failed to save.
Cancel: Stop saving all assets and return to the editor.
Retry: Attempt to save the asset again.
Continue: Skip saving this asset only.
It was working before, but when I migrated it to a new project (the one im currently using) it keeps giving me this error
I am unable to package because of it, and half of my lighting isnt built
I’ve tried force deleting it and rebuilding lighting. Exiting Epic Launcher and Editor. I’m stuck now
Help me Unreal Gods~
I’m also getting this issue. For me it occurs if I switch between a persistent level (with individually baked sub levels) back to one of the sublevels.
It also occurs occasionally when I open the project. This is a real hinderence to my workflow as the scenes then require another hour or two to be rebuilt.
I’d really appreciate an answer to this as well.
I had the same error on 4.15.3. Happened after we had a power cut during a light build 
None of the solutions I found through google helped as didn’t have 2 versions of Ue4 open and increasing file priviledges didn’t help or deleting the BuiltData.usset file. File was totally corrupted as was newly generated one.
Was getting to the point of having to consider going back to previously saved version of the project which would have meant a lot of re-work. Then lightbulb moment - I copied the BuiltData.usset file from the archived saved version of our map to my latest version. After all it would be the same if I’d kept on working without a build. Anyway success, saved fine and built map and that saved fine too.
Very relieved and happy:) Hopes this helps others in same boat.