Do I understand that you want to select a specific image to display?
If so, choose "Browse Gallery for image..."
Otherwise, can you explain what you mean when you say you "disabled" it? If you've "disabled" it, what image are you expecting when you choose "Change Desktop Image"?
I'm heading away on holiday for a month from today, so I'm not sure if I'll be able to answer any more queries for a while, sorry.
Cheers,
Conor
Christchurch, NZ
GLoSS: Gallery2 Local Screen Saver & Desktop Changer