On both Xcode 4.4 and 4.4.1 I'm experiencing the same issue in that with the specific project I'm working on, I don't seem to be able to rename any classes or variables from the Refactor menu option.
Each time I try and do a rename, I type in the new name for the class/variable and click Preview at which point the bottom left begins a spinner with Finding files.... However, I then get a message saying:
The selection is not a type that can be renamed.
Make a different selection and try again.
I'm pretty sure that this is not an issue with my specific install of Xcode, because I can refactor other projects fine, it's just that I can't seem to be able to refactor this specific project.
Anyone with any ideas? I don't have any particularly exotic configuration for this project, it just seems to be a random affliction. I've deleted all of my derived data and re-indexed, but that doesn't seem to help.
Since it works OK in other projects, I'm thinking one thing I could try to do is re-generate the actual project file(s) itself. I don't know if there is a way to do this automatically?