Sure wish my error message was more clear. I saw the same thing when trying to change to another ssd drive for installation again. The error does not really tell you “which” folder has to be empty. See image here. In my case, it turns out it’s the (lower) Engine Path folder that the installer is complaining about. So I simply renamed the offending folder from “UE_4.25” to “old_UE_4.25” and I was able to then proceed forward (…and then layer, deleting the old_UE_4.25 later).
