Updating Project Hint

If you update an Xcode project from SDK 2.x to SDK 3.x, and you get some really weird compile errors in UILocalizedIndexedCollation (or other UIKit classes) when Xcode processes the precompiled headers, the problem is probably that you need to change the compiler version from GCC 4.0 to GCC 4.2. The project templates were updated, so this isn't an issue with starting new projects, but when updating an older project, you have to manually change the compiler being used.

You can do that by selecting Edit Project Settings... from the Project menu, and navigating to the Build tab.

Look for the entry called C/C++ Compiler Version, and change it from GCC 4.0 to GCC 4.2