Using the SDK 2.1.3 RC2, I can build my app for iOS6 and iPhone 5, and they work in the simulator, as well as deploying to my attached iPhone 4S. However, when attempting to deploy to the iTunes store, the build fails.
First, it requires me to build from clean, the build python script fails on the iphone build directory being non-empty. I don't recall this being an issue in the past, but it's understandable either way.
However: After cleaning the project and attempting to build for iTunes store deplyment again, the build process fails while generating the localizable.strings file. It pauses here for several minutes, and then peters out without any error message.
Note: the project I'm building did successfully build under 2.1.2 and is on the App Store. All I've done is upgrade from 2.1.2GA to 2.1.3RC2.