Comment 22 for bug 1117292

I'm seeing this too, Ubuntu 14.04 server install on a USB3 key to a 4.4GHz machine. I agree that it looks like a race.

You don't need to explain all the ways in which this is probably a terrible idea, but since the current workaround (in #21) is involves upgrading from 12.04 to 14.04 and sounds painful, I thought I'd share what worked for me:

Boot the server installer, Ctrl-Alt-F2, open the terminal, run:

# while true; do rm /var/run/chroot-setup.lock; sleep 1; done

Then just go through the install as normal. Was failing 100% of the time before this change, works after it. Doesn't look like there are any negative consequences to the installed system.