The error message (as seen in the attachment) I am getting for updates, previous and new purchases on my MBPr, just after upgrading to Mavericks. I have cleared the cache for the Mac App Store, force closed the app store process, deleted any apps that had this error, rebooted, ensured there are no firewalls blocking connection to the app store (removed them all). I've tried with two different Apple IDs, same result. Can normally find the issue in these forums, but I'm coming up blank on this one. Any other ideas?