why this?

 From:  PaQ
2054.4 In reply to 2054.3 
Hi Rudy,

There was something really weird with this geomtry ...

In this area, the thickness of this edge is suspect,


There are even 3 edges in fact


So I separate everything, to isolate this part


The strange thing is that this geometry here is unselectable ... so I only copy/paste the valid geometry in a new file ... rejoin everything


and now the boolean works perfectly

EDITED: 3 Dec 2015 by PAQ