iTunes Connect上缺少预发布版本

Although I can upload successfully new versions of my app to iTunes Connect, I can't see them nor the previous ones under the "Prerelease" section in the app's page. Instead, I get a message saying "Upload your builds with Xcode 5.1.1 or later, or with Application Loader 3.0 or later". In the "Versions" tab, under "Builds", when I press the "+" button, I get an error saying my request couldn't be processed. Am I missing some needed configuration?Although I can upload successfully new versions