Checksum Validation Failed when submitting with Xcode 5

I had the same problem and Google led me here. From my understanding a checksum is used to ensure that the file Apple received is identical to the file you (thought you) uploaded to them.

I decided to delete my upload and try again. This worked and I didn't get the error message again. Here's what I actually did:

In iTunes Connect:

• Manage Your Apps > [your app] > View Details of the New Version.
• In the links near the top the right click on Binary Details then, on the next page, Reject This Binary. It says you'll have to prepare another upload but it's just another button to press.
• Back on the View Details page just click 'ready for upload' in the top right. It might say something slightly different but I don't want to delete by upload to double check :P
• You're now ready to upload a new binary.

In xcode:

• Go to Window > Organizer > Archives and delete the archive you previously uploaded.
• In the main window of xcode press cmd-option-shift-k to clean your build folder.
• Make a new archive and upload it like you did before. Fingers crossed all goes well.