Setting to permit user to turn off computer from session manager

[Joel Gomberg]

When I used FC2 & FC3, I could shut down my computer from the xfce4 exit 
dialog by selecting the appropriate option and entering my user 
password.  With FC4, I receive an error message that "the system 
administrator disallows shutting down the computer with your user 
account."  Does anyone know how to change this setting?  It's completely 
useless from a security standpoint, since I can quit the current xfce 
session without providing any password and can then shutdown from the 
graphical login screen without providing any password.

--
Joel