Unexpected error when connecting 2nd airport express to time machince

I have a iMac (recently updated to Maverick) with a Time Machine which I am using as my router. I have one Airport Express (Model A1392) connected (Wireless) to it to extend my network. Need to extend my network farther. Have tried adding another Express. Repeated get a "unexpected error" message when using AirPort Utility 6.3.2. Any ideas on what I need to do?

Unlike the earlier 802.11g AirPorts you cannot extend a wireless network in a series fashion. The 802.11n or 802.11ac AirPorts' extended network works in sort of a wheel fashion with the base station to be extended at the hub of that wheel. Each of the extending base station would be along one of the spokes.

The issue you are getting is most likely that the second base station is too far away (or there is too much Wi-Fi interference) from the Time Capsule that it is trying to extend.

At this point, I would recommend that you perform a "factory default" reset on the problematic Express. By default the reset will cause the Express to broadcast an unsecured wireless network with a network name of something like: Apple Network NNNNNN. Once the reset has completed temporarily connect it to the Time Capsule by Ethernet.

Your iMac should now find the Express as a new base station on the drop-down menu of the AirPort icon on the OS X menu bar. Select this base station and the AirPort Utility should start. You can configure the Express as required. When done allow it to restart, and then, disconnect it from the TC and place it at the desired location.