Gnome + KDM authentication issues

[David Cameron <sky out frontier com>]

I am having a problem when using Gnome desktop environment with KDM
display manager.  

If I try and mount removable media by clicking on it under Places, or
Places->Computer I get a pop up window telling me:

	Unable to mount location 
	Not Authorized

I can mount the media just fine from a terminal.  Also, if I attempt to
use the gui for administrative tasks, some (but not all) fail to provide
an authentication dialog, and thus I cannot perform the task.  For
example Synaptic Package Manager works just fine, but 'User Settings'
under 'Users and Groups' does not.

I suspect the answer is very simple, but I'm wearing out my keyboard
googling to no avail.

I am running Kubuntu 10.04 AMD64 and I added gnome by installing
ubuntu-desktop.  As I mentioned, I am using KDM for a display manager,
and I wish to remain with that.

I also tried installing Ubuntu 10.04 AMD64 and adding KDM by installing
kubuntu-desktop, however the result is the same for the combination KDM
+ Gnome.

Thanks for any insight you can provide