I recently bought the game and spent 2 days trying to figure out how to fix this error while waiting for customer support to get back to me. The error did not let me passed the first couple screens even to the first cut scene. My other games worked just fine when playing online and all of my xbox live ports were open on my router (I'm using the xfinity wireless router/modem combo.) When I checked my network settings, my NAT type was "Open" but my packet loss was 100%!
Some of these things might be unnecessary but they worked. Here's what I did to fix it:
1. Uninstall every part of the game. This includes profile data off of the Xbox and any add-ons
2. Go on the elderscrolls website and unlink your Xbox live profile from your account.
3. Fully power down your Xbox either by holding down the Xbox logo on your system or going to settings and doing it from there.
4. Unplug your Xbox from the power supply brick for 60+ seconds to drain any power from it.
5. Reset router to factory settings either by pressing the button or doing it remotely through your router maintenance utility in your browser.
6. Boot your router back up and set it up again. Use this site to see what ports to forward for the Xbox one:
support.xbox.com/en-US/xbox-one/networking/network-ports-used-xbox-live
7. Plug in your Xbox and boot it up. Reconnect it to your wireless and run a network test and check network settings. NAT type should be open and packet loss should be less than 5% now.
8. If everything comes up good, go ahead and install the game one part at a time. Choose to do the update after the game finishes installing and do any add-ons after the update is finished.
9. Once those are finished, start up the game and it should ask you to link your Gamertag to the elderscrolls account you should have already created. Follow the prompts and it should let you into the servers.