1. On your Mac, from the Apple Menu, select System Preferences
2. Select Keyboard
3. In the Keyboard settings, Mark the Use all F1, F2, etc. setting
4. Close the Keyboard Control Panel

In order to use the function key, hold down the Command button while pressing F7

***If the above fails to resolve: 

Oftten on Mac's, F1-F7 Keys control hardware settings (screen brightness, etc.) rather that the function key it is supposed to be in an application that uses that key. Fn works like the Shift key.

1. Try pressing Fn + F7. This tells the system to ignore the hardware assignment, and use the funcitons key within the application