How to get rid of unwanted folders in screen saver options

[aperture-apple]

Hi there,

I used to have only one folder in the selection for my screensavers, but now there suddenly appeared random pictures and folders from iPhoto, even though I changed nothing(at least as far as I know).
How do I remove them from the selection? The minus button does not work with them.

(Please do not suggest to delete the pictures, of course I want to keep those).

 

[Tumbleweed666]

What does it say in the drop down by "Source" ?