Some users have reported an issue in which music and other audio no longer play through AirTunes (remote speakers) via an AirPort Express or other setup after the update to iTunes 10.0.1.
When this issue occurs, users may not be able to select remote speakers by using the speaker button in the lower right corner of the iTunes window. The remote speaker options are shown, but cannot be selected. Users may also receive error -15000.
Check firewall settings (Windows). It appears that iTunes 10.0.1 may create extra, errant entries in the Windows firewall. Check your firewall settings for any duplicate entries and remove them, and unblock any items marked Bonjour or iTunes. Also, make sure the items are set to private network rather than public.
To access firewall settings, click Start, then Run. Type firewall.cpl, then click OK.
Reinstall or downgrade iTunes (Mac). Some users have reported that simply downloading a reinstalling the standalone iTunes 10.0.1 package resolves this issue. Failing that, you can downgrade to iTunes 9.2.1.