Problem with boolean operator, operation "Difference" bettwen two simple objects Good day, dear advanced users of Blender!
I am starting to work with Blender and have such occasion.
There two objects:
-the lighthouse and
-the cube.
I am trying to create the window in the lighthouse by using 
Boolean Modifier-> Operation Difference -> Object Cube
and immediately I have a message:
"Can't execute boolean operation" 

The *.blend file is accessible by the link
http://wikisend.com/download/612580/lighthouse.bool-error.blend

Please clarify me, how can I create the window due to this operator and 
why this error appeared?
The problem with the model is it has created double vertices


Go in the edit mode 
Press A twice to select all
Press W to bring special key and click remove double
come out of the edit mode and make boolean operation