EPERM error by launching ember server in Windows

I'm using ember 1.13.6 with node 0.12.7 and npm 2.13.2 on win32 x64. It happens frequently getting this error by executing "ember server" to launch server:

EPERM, operation not permitted 'C:\Project\my-app\tmp\core_object-output_path-UnoTIiak.tmp' other stuff ...

I have to terminate program and try again and again to succeed in launching server. When I edit my files and browser get refreshed, it happens again and I need terminate and launch server again. What is this issue?