I was having trouble submitting an app using the latest beta version of El Capitan.
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.
Zac (@twodayslate) August 27, 2015
So first, archive your app. In Xcode Organizer, right click your archive and reveal it in finder. Right click the now-revealed archive and click show package contents. Then go Products > Applications > Right Click your app and show package contents again. Now, the magic begins. Find your info.plist file. Open it in Xcode, and locate the line that says “BuildMachineOSBuild”. Alter the string from whatever it is to “14F27”. This is the Build ID for Yosemite. Safe the file, and now you should be all set to sumbit!