Eclipse - Codan fails to resolve symbol - set include path

Currently running Eclipse Luna under osx Yosemite for a C project.

I don't understand why eclipse cannot resolve a symbol.

I have an include directory I want to add, so I include it in the settings > path and symbols > include.

I can open the declaration of my symbol just fine in the editor but eclipse/codan keeps complaining that this symbol is not resolved (red underlying and no way to auto-complete that symbol).

There is something I missed I hope.

How can I solve that ?