Shadows on the wall. GLSL

Support Lighting and Rendering
1

I can not figure out the shadows on the wall. Where do these shadows come from.
How I tried to get rid of:

  1. Remove the double geometry, W → Remove Doubles

  2. Delete duplicated vertices or edges.

  3. Select all geometry, A

  4. Recalculate the normals, Ctrl+N

Clipboard01
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Blend file:

Thank you so much.

2

I found how to get rid of this strange effect: you need to clear the custom split normals data. Why this distortion happened, I did not understand.
Thank you.