SOLVED!
The problem was missing apple WWDR intermediate certificate.
We must also install the WWDR intermediate certificate issued by Apple’s worldwide developer relations. It can be downloaded from the portal or directly at
http://developer.apple.com/certificationauthority/AppleWWDRCA.cer
Make sure you add this to your keychain as well.
To add the certificate: open your keychain utility software on your Mac computer, then go to File→Import items, then select AppleWWDRCA.cer.