In my case the problem was that VC++ was trying to copy a .dll file into a system folder. Running it as administrator fixed the problem.
For anyone else that comes across this question my problem was that the target directory contained spaces i.e.
C:UsersAdministratorDocumentsVisual Studio 2017projectsblah
So for me the solution was to wrap $(TargetDir) in double quotes i.e.
copy ..resources\* “$(TargetDir)” /Y