Havent come across this but try to turn off User Access Control and then try it again
TO turn off User Access Control ( not sure if this is quite correct as I dont have Vista machine in front of me
Go to Start Settings Control Panel - User Accounts
Select your User and Select Properties
Select Turn off User Account Control
Select Ok and reboot the PC
Try it again
Also Check that you can read and write to c/Program Files/bonjour/
Open that folder and Create a New Notepad file and SAve it with some data
If you can do this then try the top thing