black faces

Hi everyone.

As you can see in the following image, I have all the normals facing out, even tried to recalculate normals outside, but these black strips keep appearing. I’m sure there are no double vertices or edges, so could anyone tell me what I’m doing wrong?

http://img33.imageshack.us/img33/6572/clipboard00k.th.jpg

gotta be doubles, or the face next to them is twisted.