Keyboard shortcuts not working

[Grant]

I have the following (default) keyboard shortcuts in xfce4:

XF86Display
<Super>p
<Control>Escape
<Control><Alt>Delete
<Alt>F2

<Alt>F2 works, but <Control>Escape and <Control><Alt>Delete don't
work.  I don't know what keys correspond to XF86Display and <Super>p
so I haven't tested those.  The commands associated with the two
shortcuts that don't work do execute successfully so I'm not sure what
the problem is.  Does anyone know how to fix this?

- Grant