Nuendo 5.5.6 and OS X Mountain Lion

I have some troubles with installing the update of N5 (5.5.6 ) when i try install the update it says " cant be opned, because it comes from not verified developer " anyone know this problem ?

Open it from the contextual menu (right click or control click on the installer). In the drop-down menu you can choose “Open” and the app will run.