I conducted a test this morning. Having the wrong sized icon for Icon-ldpi.png built just fine. If I renamed Icon-ldpi.png, the build failed, but I got build error 256 in stead of 12. That could be a Mac vs. Windows difference. But clearly if it can’t find a file named Icon-ldpi.png in the same folder with main.lua, the build will fail.
So a couple of things to try.
Rename the icon and hand type the name to avoid any unicode characters that might get put in place.
Make sure they are in the same folder as main.lua
If it’s still failing, try removing your exclude block from your build.settings.
Rob