I see this semi-regularly on Windows. I think it’s a bug or race in Eclipse, maybe a race with a virus checker which doesn’t like a delete immediately followed by a write to the same file that was deleted. The fix I use is to use Project — Clean from the menu bar.
@Ash is right in the comments above that you should not have resources in your output folder. To help avoid that, I always change the name of my output folder from “bin” to something more obvious like “eclipse/classes”