Apple Support Discussions user "JLabaree" reports:
"I just upgraded to 9.0.3 and now iTunes will not connect to Airtunes (run through a three-year-old AirPort Express). None of our three Macs will connect. The Express shows as an option on the speakers drop down in iTunes, but won't connect. This just started happening upon upgrade."It is later reported in this thread that there is no numbered error message to reference. Instead, the error only states that iTunes failed to connect to the device and a network error occurred. Troubleshooting attempts include resetting the AirPort Express units and checking the network for errors using AirPort Utility.
One possible solution comes from a thread discussing a similar issue for an earlier iTunes upgrade. User "Joe-ri" suggests:
- Open System Preferences
- Open Network pane
- Select Airport in the left list
- Click the Advanced button
- Go to the TCP/IP tab
- Set the "Configure IPv6" field to Off.
- Click "OK"
- Click "Apply"
- Let iTunes connect to your AirTunes speakers