Cannot use FN + F2 for a custom shortcut

[Robert Orzanna <orschiro gmail com>]

Hello,

I try to assign the FN + F2 shortcut (commonly known as Screensaver)
to a custom command.

This is a screenshot of how it looks like: http://i.stack.imgur.com/HScRg.png

Yet the command is not executed when using FN + F2. Any other shortcut
combination is working but not FN + F2.

Does someone have a hint why I cannot use FN + F2?

Can someone please try if he can use FN + F2 for a custom command?

Thanks,

Robert