fastlane: Testflight fails with little description, able to upload ipa through XCode

New Issue Checklist

• Updated fastlane to the latest version
• I have read the Contribution Guidelines

Testflight fails with little description why. I am able to upload the ipa file through Xcode.

Complete output when running fastlane, including the stack trace and command used

INFO [2016-10-16 16:34:03.42]: {:DEFAULT_PLATFORM=>:ios, :PLATFORM_NAME=>:ios, :LANE_NAME=>"ios release_internal_beta", :GIT_REPO_WAS_CLEAN_ON_START=>true, :SIGH_PROFILE_TYPE=>"development", :VERSION_NUMBER=>"0.1.93", :BUILD_NUMBER=>"155", :IPA_OUTPUT_PATH=>"/Users/xx/Documents/thecb4/apps/FastlanePlugin/TheCB4-FastlaneTest1/dist/TheCB4-FastlaneTest1.ipa", :DSYM_OUTPUT_PATH=>"/Users/xx/Documents/thecb4/apps/FastlanePlugin/TheCB4-FastlaneTest1/dist/TheCB4-FastlaneTest1.app.dSYM.zip", :XCODEBUILD_ARCHIVE=>"/Users/xx/Library/Developer/Xcode/Archives/2016-10-16/TheCB4-FastlaneTest1 2016-10-16 16.28.33.xcarchive", :SCAN_DERIVED_DATA_PATH=>"/Users/xx/Library/Developer/Xcode/DerivedData/TheCB4-FastlaneTest1-ghcrhchawfokctfloxefohhomzsd", :SCAN_GENERATED_PLIST_FILES=>["/Users/xx/Library/Developer/Xcode/DerivedData/TheCB4-FastlaneTest1-ghcrhchawfokctfloxefohhomzsd/Logs/Test/BF5A146A-D0AB-4C9F-8B30-EA942F58C9B6_TestSummaries.plist"], :SCAN_GENERATED_PLIST_FILE=>"/Users/xx/Library/Developer/Xcode/DerivedData/TheCB4-FastlaneTest1-ghcrhchawfokctfloxefohhomzsd/Logs/Test/BF5A146A-D0AB-4C9F-8B30-EA942F58C9B6_TestSummaries.plist"}
ERROR [2016-10-16 16:34:03.42]: {"data"=>nil, "messages"=>{"warn"=>nil, "error"=>["Unexpected Error"], "info"=>nil}, "statusCode"=>"ERROR"}
INFO [2016-10-16 16:34:03.42]: Successfully generated documentation at path '/Users/xx/Documents/thecb4/apps/FastlanePlugin/TheCB4-FastlaneTest1/fastlane/README.md'

Configuration Files

Please copy the complete content of your Fastfile and any other configuration files you use below:

Fastfile:

  desc "Push ipa to iTunes App Store"
  lane :push_app_to_testflight do
    whattotest = File.read("metadata/testflight.txt")
    testflight(
      changelog:whattotest,
      ipa:"./dist/#{config["app_name"]}.ipa",
      skip_submission: false,
      distribute_external: false,
      verbose: true
    )
  end

Environment

fastlane version (run fastlane -v): fastlane 1.105.2

Do you use bundler to execute fastlane (i.e. bundle exec fastlane)? Yes

Do you use a Ruby environment manager (e.g. chruby, rbenv, rvm)? rbenv ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin16]

What Xcode version do you use (e.g. 7.3, 8.0) 8.0