Well iTunes 10.0.1.22 was released this weekend and it appeared to cause some people problems streaming to their AirPort Express devices. I stream iTunes almost everyday so this is a huge issue in my house.
I had no problems connecting to my AirPort Express in iTunes, but each and every time I attempted to stream music I would receive an error message “cannot connect to remote speakers unknown error (-15000)”. I tried streaming from another laptop with the original iTunes 10 installed and I had no problems. After checking my network and making sure I had my AirPort Express firmware up to date I called Apple.
I spent about 40 minutes on the phone with an Apple support supervisor and provided diagnostic log files from iTunes. Well, not being one that likes to sit and wait for a solution I started to mess around.
I decided to see what would happen if I upgraded iTunes on the other laptop… Low and behold it worked and streamed to the AirPort Express just fine. So……I reinstalled iTunes 10.0.1.22 on my laptop That did not work.
Next, I uninstalled iTunes, restarted the laptop.
Then manually downloaded iTunes from apple.com.
Then, installed iTunes, but did not run iTunes instead I restarted the laptop after the install completed.
Finally, after the restart and launch of iTunes I was able to connect to the airport express and stream music!!!
So at the very least I would suggest to do an uninstall then reinstall. The restarts may not be necessary, but just for the sake of completion I would suggest those be included in the steps.