Hmmm...
1. Maybe your graphics card doesn't support cubemap/bump maps? Be sure that your graphics drivers are up to date, an answer you might get way too often.
2. Is it only that one texture doing that? Is it only that map?
3. Try in console:
mat_bumpmap 0
mat_specular 0
You'll lose some quality but it may fix the problem. Also try messing with those values because I think having specular=1 but bumpmap=0 can make the problem you are having.