bcbc appears to have essentially answered the question in a comment:
The 'backend' error is a wubi bug, but it only occurs after the ISO is
rejected. So there is likely a problem with the DVD (which explains
why you can't boot from it) and perhaps the ISO (which might explain
why the USB stick fails as well)
– bcbc Feb 28 '12 at 17:42
So the error only happens after Wubi looked at the files on the CD and found it not to be the right file. This is usually due a corrupted or damaged ISO or CD/DVD/USB, so:
- MD5 test the ISO image. If it's bad, download the ISO again (and MD5 test that one too).
- If your DVD and USB flash drive were created from an ISO image with a valid MD5SUM:
- Make sure you are writing the USB flash drive and burning the DVD correctly. Try making them again. (You'll need a new DVD but you can use the same flash drive.)
- Try burning the DVD at the slowest possible speed. This can sometimes reduce the risk of errors, or of physical damage to the DVD's surface if your DVD media are not entirely compatible with your DVD writer. (This applies to CD's too, to a degree.)
- That should let you install a normal Ubuntu system, alongside (or in place of) your Windows system. I recommend that, as it performs a bit better and is considerably easier to fix if something goes wrong. However, if you prefer to use Wubi, you can install without having to prepare a CD/DVD or USB drive at all. Just make an empty folder, and put the ISO image and
wubi.exe in the folder. (You can get wubi.exe here.) Then run wubi.exe.
Also please note that if you're able to boot an Ubuntu CD/DVD or USB flash drive, you can test the burn/write itself using this method (also explained here). This is highly advisable, especially if you've already experienced problems like you have.
