From your screenshot, it looks like the left side is a solid wall and the light is shining through instead of casting a shadow right? So the only shadow I see is from the left front edge. If that's the case, then I think you should check your normals. It looks as though the normals on one of the faces of that side wall is facing the wrong way which would definitely cause that.
That's all I can think of right now that might cause that.
Edit: Attached a screenshot. The left wall has the left face normal reversed which is allowing light to pass through the wall. However, it's pretty obvious because if you were to look at that left wall from the left side, it would look invisible. I don't know anything about lightmaps so as was already mentioned, might want to double check to make sure no part of the light uv is outside the 0,1 space.
Don't be satisfied with what you can do but rather strive to do the things you can't do!
Last edited by Perfecto; 06-01-2012 at 04:23 PM.