Before Xcode 6, it was sufficient to provide only a *.p12 certificate and *.mobileprovision file to Xcode in order to export an *.ipa file for Ad Hoc builds.
Xcode 6 ope
This solution worked for me.
https://stackoverflow.com/a/26497744/1500634
Xcode Version 6.1 TestFlight Version 1.0 (320)
Download a previous version of Xcode, I just got the version 4.6.3 and it worked fine so far.
https://developer.apple.com/downloads/index.action