title: iOS app submission yields "invalid toolchain" although Xcode is up-to-date
body: <p>I have submitted my app to the app store using Xcode 6.4 on OS X 10.11, the app was pre-approved for testing. I then iterated through 5 builds all of which were uploaded successfully and installed on multiple test devices. Now that I am trying to submit for the final approval, I am getting:</p>
  
  <p><code>"Invalid Toolchain. New apps and app updates must be built with the public (GM) versions of Xcode 6 or later, and iOS 8 SDK or later. Don't submit apps built with beta software.
  "</code></p>
  
  <p>How can this be given that I am using Xcode 6.4, the app is set to run on iOS 8 or greater, and all of my previous builds, including the current, have been just fine getting into the test program and being installed?</p>
  
  <p>Does anyone know how I could rectify this situation to get my app into the final step?</p>