Same here, 2.53 r30581. I replaced the light again and it didn’t seem to change anything.
Edit: As loopduplicate said, a lot of the problem seems to be in the modeling/topology. For example the face normals are pointing in random directions. Sometimes this happens when you do a lot of scaling and extruding of vertices from a plane. Some of that can be corrected by removing doubles, then using Ctrl-A in object mode to ‘Apply Scale.’ However you might be better off starting over with this model, now that you have the practice after being through it once.