If you have a black skybox when you select any of the "default_..." SSIs then this post can help you.
1. Open APE (the monkey head)
2. tick the checkbox for "GTD" in the filters and search for "ssi" and scroll to ssi in the window about the filter
3. select any of the ssi that doesn't work
4. look for the box where the adress is and click on the blue arrow right next to it
5. tick the checkboxes for "German Unsafe", "Japenes Unsafe" and "Arabic Unsafe"
6. save the file with CTRL + S
7. open your map
8. select your volume_sun and open the entity_info with N
9. select the edit ssi
DONE!