crazy Black areas on some objects

hello blender people.

I am using blender since 1 month and this problem appeared a few times.
I modeled an elevator shaft. but if i render the image, i get some really confusing lighting problems. Some objects have black pixels on them. i tried everything, but it just doesnt go away.

I put 2 pics in that you can see.:eyebrowlift: look at the rails on the right side and bottom middle.

i hope you can help me out.
(i couldn’t upload the .blend file, error all the times)

Raphael from switzerland


Looks like overlapping faces. Check you haven’t two duplicate objects in the same location. Otherwise select all the vertices in your object and W / remove doubles, then recalculate your face normals with Ctrl+N

Thank you. it really works. i knew the removing doubles trick, but i didn’t know that you have to do it in Edit mode and with all the vertices selected.

your Raphael