I upgraded my OSX from Snow Leopard to Lion and I downloaded Xcode 4.3.1 Now when I try to validate and publish my app I get the first screenshot. If I click on Download Identif
These steps solved it for me (some of them are in the answers above):
I was very glad that I didn't have to revoke everything in the Developer Portal.
My announcement to Apple: Please, make this process much more easier and bugfree! It's such a hassle that costs me hours every time you force me to update to a new MacOS, Xcode, iTunes, iOS in order to keep my software running!