several people have updated directly to 2.0.1 from 1.x, which was designed to fail, but failed to fail correctly. (new thread idea: “failing correctly”) 
here’s how you recover. it involves terminals.
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on your laptop, download norns190405.tgz and copy it to a FAT-formatted USB thumbdrive. make sure your browser doesn’t uncompress it. make sure the filename is norns190405.tgz
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insert the thumbdrive. power up norns.
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connect via serial (which is also described at https://monome.org/docs/norns)
- connect usb cable from norns power to laptop
- run Terminal.app
- type (but do not press enter)
screen /dev/tty.usb
- press TAB. this will autofill the rest of the path, which will look something like
tty.usbASDF23
- complete the line with
115200 so it looks like
screen /dev/tty.usbASDF23 115200
- press enter. you should get a blank screen. press enter again. you’ll get a login prompt. user:
we password: sleep
- time to run the update. copy-paste these commands line by line and push enter. none of them should fail. if they fail, something didn’t work right.
cd update
cp /media/usb0/norns190405.tgz .
tar xzvf norns190405.tgz
tar xzvf 190405.tgz
cd 190405
./update.sh
the update will run now. when done, shut down norns.
sudo shutdown now
you can close the terminal.
reboot norns and you’ll be at 2.0.0. you can then use SYSTEM > UPDATE to get the newest version.