I have one of my long standing projects which I was attempting to build with the new 2.7 version / Joomla 3.2 version, it kept failing with

Which I assumed was just a broken FK I needed to track down. This error also occurred in other versions of the build (2.6.5 legacy)

I made a copy of the project (OMG I LOVE THIS FUNCTIONALITY!!!) as I just wanted to do some draconain removals to try and track down what FK was potentially causing the problem.. but oddly enough the copy seems to build fine with no errors with NO changes made?!

The project is the one that begins with the name 'Pin....' (branded name, don't want to mention the full name in a public forum). Is copy a project and deleting the old one going to be a necessity for projects or is this just a wierd one off? I have not checked the new copy to make sure its all there beyond counting the tables

Yes, because when you lone the project, it also remove all inconsistencies such as broken paths.

I have putted a check so now it is fixed and you can build.