802.11ac TC setup: "An unexpected error occurred. Try again."

Question

I am attempting to replace an older 2TB 802.11n Time Capsule that was working fine with a new 3TB 802.11ac Time Capsule. I have followed the instructions, setting up the new TC just as the old one was set up. However, all I can manage is to get this error message: “An unexpected error occurred. Try again.” I have tried more than a dozen times, including various configurations, to no avail. I have returned to using my old TC until I can resolve this issue. I am using a Motorola SurfBoard SB6141 cable modem. Please advise. Thank you.

Answer 1

Power off the modem completely by pulling the power cable from the back of the device, or from the wall AC jack. Leave it off for at least 30 minutes....longer would be better.
“An unexpected error occurred. Try again.”
This is a common message in Yosemite due to glaring bugs in the networking software. Please try the following....which may help...and may not.
On your Mac....open System Preferences (gear icon on the dock)
Open Network
Click on WiFi on the left to highlight it
Click Advanced at the lower right
Click the TCP/IP tab
Make sure that the setting for Configure IPv6 is set to Link Local Only
Click OK
Click Apply
Repeat the same sequence as above, except this time click on Ethernet and follow the same steps all the way through
Restart the Mac
Power up the new Time Capsule for a minute or two
Hold in the reset button for 8-10 seconds and release
Allow a full minute for the Time Capsule to restart to a slow, blinking amber light.
Power off the Time Capsule
After the modem power down period, connect the Ethernet cable from the modem to the WAN "O" port on the Time Capsule
Power up the modem, and let it run at least 10 minutes
Power up the Time Capsule and let it run 2-3 minutes
Click the AirPort icon at the top of the screen and look for a setting of New AirPort Base Station
Just below that, click on Time Capsule
The setup utility will open up and analyze the settings, then suggest that the Time Capsule be configured to create a new network.
Follow the prompts. You can use the same wireless network name that you used before and the same password if you wish.
Be sure to assign a new device name to the Time Capsule....something simple.  For example, mine is TC.  Do not use the name that Apple suggests.
I would not recommend that you try to use the option in AirPort Setup to have the new Time Capsule replace the old Time Capsule.
No guarantees, but you have our best shot based on experience. Good luck!
If you continue to receive the "unexpected error" message, we can try the setup on an iPhone or iPad, which ofter works better than a Mac. Otherwise, please contact Apple Support, as there is nothing more that we can do.