Help Please: shadowed texture on right angle prim

I'm a beginner builder and I'm working on a small furniture peice, I've used the triangle (right angle) prim in the peice of furniture and for some reason it's got this odd shadow on it >_< I have no idea how to get rid of it, it remains even though I've textured the chair.. there's a picture below. any suggestions?
http://www.pixelated-pony.net/chair.jpg

Yea. I got the same effect when the sunlight is hitting that side of the prim. Here's how to fix it from what I found to work. Change the "Top Size" of the triangle prim to 0.01 and it's gone. Size 0.00 seems to have an odd shadow bug.

woot, all fixed - thank you so much!