i'm trying to add my airport express to my network. The airport utility shows a message that its gathering info about my network then suddenly an unexpected error message appears. Why is that?

We need a bit more information to be able to start the troubleshooting process here.

What device are you using to try to setup the Express? A Mac, or an iPhone/iPad?

If a Mac, what operating system is the Mac running? If you are not sure, click the Apple icon in the upper left corner of the screen, then click About This Mac and post back with the OS X version that you see there.

What service will the Express provide on your network? Or, in other words, what will the Express do?

Do you have a spare Ethernet cable handy....any length will do....in case that might be needed for the setup?

Until Bob Timmons gets back to you, first decide what you would like the Express to do. I understand you want it for AirPlay remote speakers, which you can certainly do.

I am assuming that you are not using an Apple AirPort router; if that's not the case stop here and let me know.

If your existing router is not an Apple AirPort Base Station, the Express:

• can "join" an existing wireless network as a client, for the sole purpose of streaming music. If that's what you want to do, do not connect it to your router with an Ethernet cable.
• can "extend" an existing wired network to serve as an additional wireless access point, which can also stream music. If that's what you want to do, connect its WAN port to an available LAN port on your router using an Ethernet cable.

Then, "hard reset" the Express according to the instructions below, and configure it. The prompts should be self-explanatory. If you run into trouble, describe which of the above two configurations you decided upon, and the point at which you're getting the "unexpected problem".

To "hard reset" an AirPort Base Station: make sure it's powered up, then gently press and hold its tiny reset button. Don't apply any more force than required to feel a tactile click. Keep it depressed for five to ten seconds, long enough for its LED to flash amber rapidly. Release the reset button. Then, the LED will glow amber steadily for about a minute. Then, it will flash amber, slowly, about once every second or two, waiting for you to configure it with AirPort Utility.

If the Express's LED is flashing yellow, slowly, that indicates it's ready for you to configure it using AirPort Utility. If it isn't, perform another "hard reset".

You need to specifically join its network by selecting it in your Mac's Wi-Fi menu. Depending on your OS X version, it will either appear as "New AirPort Express..." (recent OS X versions) or "Apple Network nnnnnn" (earlier OS X versions). That is a temporary open network it creates for the purposes of configuration. Select it, and then use AirPort Utility.

During that time you will no longer have an Internet connection, because your Mac will be connected only to the Express.

After you configure it and resolve any configuration errors that may result, click Update. As the Express restarts, the temporary open network it created will cease to exist, and AirPort Utility is likely to report "An unexpected error has occurred". The reason that happens is that the Express is no longer creating a network in Client Mode and will no longer appear in AirPort Utility. At that point, just quit AirPort Utility and re-join your existing wireless network by selecting it in your Mac's Wi-Fi menu. The temporary Express network may remain visible in that menu for a while, but it will eventually disappear.

The Express's LED should illuminate solid green, and its speakers should then appear as an output option in apps that support AirPlay streaming such as iTunes.

As you might imagine using a non-Apple router complicates things a bit, and since I don't use one of them I am unable to provide more specific instructions. What you propose is certainly achievable though. Let me know if you still get stuck.

John Galt wrote:

... The reason that happens is that the Express is no longer creating a network in Client Mode and will no longer appear in AirPort Utility.

Keep that in mind if you should ever need to reconfigure the Express. I don't believe the Express will appear in AirPort Utility after it is configured as a wireless client, so to reconfigure it in the future will require repeating the "hard reset", joining its network, etc.

This Apple Support document may help explain in greater detail:

AirPort Express: What is client mode? - Apple Support

It's simply AirPort Utility trying to be too clever, by suggesting the password used by the previous router. By default, a new Express has no password so try deleting that password (highlight it then press the delete key). AirPort Utility should establish a connection to it for the purposes of configuration. Bear in mind while doing that your Mac will be communicating directly with the Express and not your router. No password will be required.

If you're still frustrated, call AppleCare. Since your Express is brand new, support is free. I believe they are now available on weekends so if you're in the US you can use the link under Contact Apple Support. They'll even call you back at a time convenient for you. Complete all the information using that link first, so that they will understand what you need before they call.

Have the Express's serial number ready - it will appear in AirPort Utility, assuming you can establish a connection to it. Just click the Express's icon and its serial number will appear in a popup window.