Mesh Difference Error

Hey Guys,

I am having an issue when I try to mesh difference the meshes shown below.

I want the resulting mesh to be the right mesh shaped by the left one. However the result 'Mesh difference' give me is 

shown in the second image. 

It should be a simple mesh difference operation no?

Thanks in advance! 

Stavros 

to be The result that comes out (image below) is not what I want