Wavelab 10 - Edit Project (Source)

If I choose an audio file to edit in Wavelab 10, in the EDIT tab there is a tab button called SOURCE (Top left) with the inscription ‘Edit Project’ this is always greyed out.

The manual says its use is to update the associated Nuendo/Cubase project file, which sounds cool, but what do I have to do to get this button active and not greyed out?