Light problem with cubes

I have some instantiate cube prefabs(simple cube with a diffuse shader) in my scene forming a wall. and I added a point light to light them. But they show a strange shadow. I would like to light them as a Wall ant not like single cubes. What shgould i do to light them as one object.

See the picture for details:
http://www.premiumforce.de/1/light.jpg

PROBLEM SOLVED:
first select the prefab in your project window and look in the inspector(model tab)

set normal to “Calculate” and tangents to “Calculate”

that worked for me! Oh I am so happy!

You don’t appear to have any rigidbodies on your cubes, so im assuming you just want an unmovable wall.

Use the scale in the Transform Component to increase the size of one block to make a single wall.

Put the same material over that wall and change the Tiling(x and y) to make the material look flush with the old wall.