Random instance of object illuminating. i.e, random object glowing.

the link above shows my prototype layout for a classroom. i designed the tables using blender. however, when i build lighting, at least one of the desk is illuminated. If I delete that copy and duplicate another copy, the problem is fixed. However, another copy of the desk which is already on the map starts glowing.
Given below is the material i used for the desk stand.


Come on guys… Someone, help!