I wanted to add that I had the same issue, but I didn't get an error code. It would just go through the update process three times in a row, then the TV would no longer read the unit so I would have to unplug the Roku Express and plug it back in.
I went through this process for an hour, then went looking for troubleshooting info, and found this post. Using the Secret Screen referenced in the original post, I tried manual update (no luck), factory reset (still had the same issue), and tried cycling the update (this did nothing). I had an IP address. I have a Roku Streaming Stick, a Premiere, and a Roku TV, and this was the first unit that I've had any issues with.
FINALLY I tried to use my mobile hotspot and that worked. By this point I had been working on this for close to two hours. I was ready to chuck this thing as far as I could throw it. It wouldn't have solved anything, and I would have had to fish it out of the snow, but I thought I'd feel better.
Once I updated the software and registered my device, I disconnected from the hotspot so that I could connect to the wireless network in my home. Now, even though it could find it before I did the update, it now cannot connect to my network. I tried restarting my Roku. The TV no longer could find the signal after restarting, so I had to unplug the Roku and re-plug it back in. Still cannot connect. I tried rebooting the router, then rebooting the Roku. Had to unplug it again and re-plug it back in. Still won't connect. Tried restarting AGAIN. AGAIN, I have to unplug/re-plug the unit. Tried rebooting my mesh wireless node as well. STILL WILL NOT CONNECT. I go to the Secret Screen. Now, I don't have an IP address showing like I did when I started this process.
This is supposed to be the EASY Roku! This is insane that I have spent 2.5 hours at this point trying to install a simple dongle. No Ethernet option, so I cannot check that. Everything else in the house hooked up to wifi and the router is working fine. I don't get it. No customer service support, either.
I think I have to take this one back and say the heck with it. I don't want to spend $40 on the next one up.
UPDATE: I finally got it working! I restarted it one last time (again, plug/replug to get the TV to read the signal after restarting) and checked my Circle (parental controls) settings. I added the Express to my home devices. I'm not sure which one worked; I'm just happy it finally works now.