I know what the problem is, I was having the same one not too long ago. Download this scope, and you'll notice there's an extra file, called a "shader." If you take it out of this scope and stick it in yours with the right directories, it'll work.
http://www.alliedassault.com/pafiledb/p ... le&id=2132
Just look at how this guy set his up, and copy it exactly.