not authorized to execute this service

Hi List,

I installed an ltsp server for my users with kubuntu and I use kiosk to give 
them a default start menu and keep users in their homedirectories. Everything 
works fine except the desktop shortcuts. Shortcuts to folders or websites work 
but shortcuts to applications don't. When I want to start for example 
thunderbird from the desktop shortcut I get "You are not authorized to execute 
this service". This is a kiosk problem because users that are not in the kiosk 
group don't get this error.

Thanks