A few people who have installed the latest version of iTunes (version 10.0.1) have found that their remote speakers are no longer working. This reflects similar reports that came out when people upgraded from iTunes 9.2.1 to the initial release of iTunes 10.
The problem may be hard to pinpoint, but so far people have had success in turning off the system firewall or reinstalling the program; however, removing relevant preference files may also help.
Toggle or turn off firewall
To turn off the firewall, in OS X 10.5 Leopard go to the Security system preferences and select the option to allow all incoming connections. In Snow Leopard just click the Off button in the Firewall section of the preference pane.
Optionally you may wish to clear your firewall settings and start over allowing or disallowing various applications from receiving information from the Internet. This can be done by removing the "com.apple.alf.plist" file from the /Macintosh HD/Library/Preferences/ folder and restarting the computer.
Reinstall the program
Quit iTunes 10 and remove the application from your Applications folder. Then also remove the "com.apple.iTunes.plist" and "com.apple.iTunes.eq.plist" files from your /username/Library/Preferences/ folders. After this is done, use a cache-cleaning utility like OnyX to clear the user application caches, and restart the computer. Finally, download the latest version of iTunes from Apple's Web site and reinstall it.