I know this an older post, however, I’ve made this issue occur with the above reported errors even in version 4.7.3 (currently latest version), and the reason is very simple:
It’s because you were trying to run in editor mode using .pak file data. The editor wants loose data files. I get this issue if I was running a development build using a .pak file, switch to editor build but forget to remove the .pak file command line parameter. Just remove the .pak file params and it would run fine.