Well, I found this problem a few minutes ago… I was trying the new version of Blender, when I found this: (image) Everything’s allright, the cube has “Light” “Doublesided” faces, and it works great… but not in the runtime. Any ideas? 
COngratulation you made the third topic about the same thing again (please use search before creating a topic)
08/09/08
http://blenderartists.org/forum/showthread.php?t=135080
25/08/08
http://blenderartists.org/forum/showthread.php?t=133970
EDIT: DAMN YOU CYBORG
What? Expecting people to make an effort and use the search button… naah too much to expect 