Can't change startup programs in Startup Application Preferences
Solution 1:
It sounds like a permission problem, you can try this (from a terminal):
sudo chown [username]:[username] -R ~/.config
If it doesn't help, try to start the "Startup Application Preferences" from a terminal using this command:
gnome-session-properties
You might see relevant error messages there. If the output looks useless to you, you might post it here.