My buddy updated his iTunes to v10 when it came out and completely lost Airport Express music streaming on his XP machine. I upgraded to v10 as well and had no issues streaming from Windows 7 Ultimate--and in fact my Airport Express streaming was more stable with that version.

However, I just upgraded to the newest 10.0.1 which completely killed my Airport Express streaming from iTunes with the 15000 unknown error. My fix was to uninstall, then do a System Restore and reinstall of v10 which worked. My fallback would have been to do a full System Image Recovery.

Does anybody have any feedback as to what is killing the Airport Expresses streaming ability? All the firmware updates are current and my buddy and I have different brands of wireless routers.