Comment 17 for bug 1208129

I hit this bug when I tried to make a USB boot stick using an ISO I created by following https://help.ubuntu.com/community/LiveCDCustomizationFromScratch

Fortunately usb-creator-gtk is written in python, so I found the code which was catching the exception:

  dpkg-query -L usb-creator-common usb-creator-gtk | grep \\.py | xargs grep -H uncaught

and commented it out(vim /usr/lib/python3/dist-packages/usbcreator/install.py...). That allowed me to get a normal backtrace when the failure occurred:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python3.4/threading.py", line 920, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3/dist-packages/usbcreator/install.py", line 156, in run
    self.install()
  File "/usr/lib/python3/dist-packages/usbcreator/install.py", line 624, in install
    self.install_bootloader()
  File "/usr/lib/python3/dist-packages/usbcreator/install.py", line 251, in install_bootloader
    self.need_syslinux_legacy(),
  File "/usr/lib/python3/dist-packages/usbcreator/install.py", line 225, in need_syslinux_legacy
    return our_os_ver >= '10.10' and target_os_ver <= '10.04'
TypeError: unorderable types: NoneType() <= str()

Which led to the following function at line 225:

    def need_syslinux_legacy(self):
        target_os_ver, our_os_ver = self.os_vers()
        return our_os_ver >= '10.10' and target_os_ver <= '10.04'

So it looks like self.os_vers() is returning None. After adding a few debug prints, the problem turned out to be that self.os_vers() was having trouble parsing my .disk/.info file, which, as suggested by https://help.ubuntu.com/community/LiveCDCustomizationFromScratch, was "Ubuntu Remix".

Changing the value in .disk/.info to "Ubuntu Remix 14.04" seems to have fixed the issue for me. There are lots of ways to trigger this bug, I think, so there's no guarantee this will work for you.