Hmm… There are two possibilities I can think of here. First Try looking for any null Object actors in your level. These are actors which appear in the World Outliner but actually have no mesh or BP associated with them. Delete any of these you find. They can cause issues with Light Builds.
If that does not work, try deleting your Intermediate, Saved, and Derived Data Cache Folders in your Projects Folder. This will require some Shader and Code recompiling but, often will clear up an corrupted data that has been incorrect stored there. Since you are able to build another map I am thinking something has gotten corrupted in the problem level and often clearing these directories and allowing a rebuild can solve the issue.
Let me know again if the Log Changes-
Eric Ketchum