Unknown Error

Anyone have any idea on what's going on here and how to resolve this problem?

Yes. Airtunes streams music through UDP port 5353. You probably have a firewall that's blocking communication through this port. Read this knowledgebase article:

Error -3256 or -15000 when streaming to AirPort Express base stations using iTunes

Unfortunately the document only refers to OS X, and I can't find a corresponding one for Windows. If you can muddle through Windows enough to determine how to open UDP port 5353, it will most likely solve your problem.

Here are a couple of things you might try, though Norton Internet Security might change this. You might try disabling it for the time being.

Go to start menu > Control Panel > Windows Firewall. Under the General tab, you can select On or Off. Assuming it's On, and "don't allow exceptions" isn't checked, click on Exceptions, then click Add Port... Name this port Airtunes, provide port number 5353, click UDP, and click OK. This takes you back to the last window where you might consider checking the box where it says "Display a notification when Windows Firewall blocks a program" which might help tell you what's happening in the future.

Click OK again and you're done.

On my Windows computer, I already had that port enabled, but I've installed Apple's Bonjour for Windows so I never had to create it. You might try installing that in lieu of the above.

I am having the same problem, Error -3256, but None of the suggested solutions have worked. I am running Windows XP, Bonjour for Windows, and have Norton Security running. Are there any new ideas about a solution.

I fixed my error -3256 problem by downloading the newest version of "Airport Utility" (V. 5.3.1) and downloading the most recent software updates to my AEX. I think that the firmware v6.3 upgrade my have done it. My AEX has never performed as well as it does now.
My AEX was first purchased and installed in 2005 and I had only kept up with the newer versions of Itunes but not the updates to my AEX. The CD that came with the AEX only provided an "Airport Adm. Utility" which did not automatically search the internet for software upgrades for AEX like the the newest version of "Airport Utility" does. mt

Ditto for me.

I was getting the -3256 Unknown Error and was about to replace my Airport Express. I unchecked the "Block UDP Traffic" and now it works.

Thanks for the suggestion.