I'm trying to install Ubuntu Server 14.04.2 on an old Athlon 64, but as soon as I get past the initial menu, choosing to install Ubuntu Server, I get some console output and everything gets stuck on:

mount: mounting /dev/sda on /media failed: Invalid argument

umount: can't umount /media: Invalid argument

mount: mounting /dev/sdb on /media failed: Invalid argument

umount: can't umount /media: Invalid argument

I used the exact same USB stick to install on another box. I couldn't find anything else about this error other than this topic, where one user claims it eventually works, but in my case I left it sitting there for almost an hour and nothing.