Do you have a folder named Resource or Resources? Rename that to a different name and try again. (Remember to clean the project.)
EDIT: If this does not fix it, look at the project settings, there under "Build phases" and there under "Copy Bundle Resources". Maybe a stale entry sits there and needs to be removed manually.
EDIT: Also clean the project. Hold the option key when clicking on the menu entry so it says "Clean Build Folder...". If necessary, remove the derived data: Open Organizer, select your project: There is an entry "Derived Data" which shows the path to the files generated by Xcode. Right to that is also a Delete button - click that to delete all the derived data. (Xcode will have to rebuild index files etc., nothing critical)
(I remember, that I saw such errors when I had a Resource(s) folder and when I renamed it, it worked again. As far as I understood, Resource is used for Mac OS X apps. I assumed it would not be used for iOS, but at least it caused trouble in my case.)