The latest Lion update (10.7.3) causes Apps which are archived and then validated using the Xcode organiser to fail, with the following warning:
iPhone/iPod Touch: Icon.png: icon dimensions (0 x 0) don’t meet the size requirements. The icon file must be 57 x 57 pixels, in .png format
Don’t panic, you are not going mad – there is nothing wrong with your App Icon size – this is a bug as a result of the Lion update. To fix it, download the latest version of the Application Loader from here.
Once it has downloaded, quit Xcode, install the new Application Loader as normal. Restart Xcode, and generate a new archive for distribution. When you validate this new archive, all should be well.