http://stackoverflow.com/questions/577750/running-xcodebuild-from-a-forked-terminal/581002#581002
solution :
‧Open the Keychain Access
‧Right click on the private key
‧Select “Get Info”
‧Select “Access Control” tab
‧Click “Allow all applications to access this item”
‧Click “Save Changes”
‧Enter your password
‧Enjoy