Xcode 4.3.2: Can't add files outside of project folder

I just upgraded to XCode 4.3.2 and now my old projects are not loaded correctly. All files outside the project folder are displayed in red. The folder structure is as follows:

• MyLibFiles
  • mylibfile.h
• MyProject
  • MyProject.xcodeproj
  • anysource.h
  • alias mylibfile.h

Therefore I cannot add "mylibfile.h" to the project. This is simply not possible. It is also not possible to add a file via an alias ("mylibfile.h alias").

Currently the only way to make a copy of "MyLibFiles" is in "MyProject". But this cannot be so, it is stupid.