Help Please Unknwon Black shadow

[vshvjt1]

Hello guys.
Look in image why this unknown shadow is appearing in game ?

This shadow is visible if i will add more than 2 objects (Brown color object at left side)

Thanks please help me fast

[BoostedFridge]

The picture shown is in the world editor. Does the shadow appear when you actually go into game here?

[vshvjt1]

Yes (Its show also in game)
actually i created this object simple box. without any shadow object. when i will place upto 3 then this shadow will appear.