I upgraded my OS X to Mavericks and the install was very smooth. Since then, however, I cannot update any apps or purchase new ones in the App Store. I receive a message saying "Failed to verify the preflight file. It is not signed by Apple. The application will be available from the Purchases page." Unfortunately the same thing happens when I use the Purchases page as well.
Am I doing something wrong or did something break with App Store after my installation?