Airport Express in bridge mode not working after update to 7.8

I have 2 Airport Express units. The first is connected to my cable modem via ethernet. My second is connected wirelessly to the first in bridge mode. I've had this set up for a few years with little problems. Today I updated both AirPort Express units to 7.8 via the Airport Utility on my Mac - which I've done before over the years. The unit connected to my cable modem updated fine. The second unit still flashes amber, and the message I receive when I click on the status is:

Extended Network

This Airport Base Station was unable to extend the wireless network. Make sure the wireless network you're trying to extend was set up and is working correctly, that you entered a matching wireless network password into this device, and that this device is in range of the wireless network.

Since I've changed no settings, and did nothing but update the firmware, I am at a loss of how to fix this or what I need to do to clear the error. I've tried unplugging the unit and plugging it back in, I've tried ignoring the status (which took the unit off the network as shown in the AirPort Utility on my Mac - but reappeared once I unplugged and replugged in the unit).

It's probably obvious that I am not a tech person - and I am at a total loss. Does anyone have any suggestions? Thank you!