"An unknown error occurred (-15000)."

I've got a brand new Airport Express and I', trying to set it up for the first time and I'm getting the same message. I've got a Airport Base Station Extreme and all I want the Airport Express to do is play music form iTunes to a remote receiver. I've got a green indicator light so that is not the problem. I've tried two different receivers and I get the same error message when connected to either one. Any ideas? Thanks.

I have the same problem, read at another section of this forum to try the following:
Open System Preferences. click on "Network"
Highlight "Airport connected" and click on "Advanced...." find "TCP/IP" go to "Configure IPv6" and turn it "Off"
Click "O.K" THEN FINISH WITH CLICKING ON "Apply"
this fixed the problem for me.

Thanks, that fixed the problem. I now have music where I want it.

This problem has just started since iTunes 9 and AppleTV 3.0

I don't want to turn off IPv6 because isn't that what Back To My Mac uses?

I need both functions to work as they did before

@emu201 Thanks for your suggestion.
Have the same problem as most of the others described with similar configurations (timecapsule + airport express) / softwareversions (all latest - itunes 9.0.2).

For your information - solution worked for about 10 seconds (after stopping and starting the wireless network), then lost the connection again.
Changed everything back to orginal settings - IPv6 automatic - and now it works again; wonder for how long. Bit dodgy.

Seems that there's no definite solution yet, so still looking for other solutions (besides downgrading itunes/ Snow Leopard to a previous version).
More ideas anyone?

Thanks!