Right, it has to do with Codesign v2.
Since 1.2.2015 you need an apple developer account for iOS, resign the ipa and then test it. :/
We show, that we can make this process easier and we 're adding arm64 (which was now needed too from apple -> to pushlish it on the iOS Store) too.
With Codesign 1 (before 1.2.2015) it works without resign the IPA to test it on the iPad.