I\'m using command line xcodebuild tool to export ad-hoc distribution ipa file out of my archive like this:
xcodebuild -exportArchive -archivePath /path/Arch
This forum helped me to fix the issue. https://forums.developer.apple.com/message/59201#59201
SOLUTION: change the key from 'method' to 'export_method' in the exportOptionsPlist.