@Andrew Henry: the issue is that some udeb files in the Ubuntu alternate iso have more than 64-character filenames, but unfortunately they are truncated to 64 characters (and hence can't be found by the installer) because 7-zip, which is used by UNetbootin for extracting iso files, doesn't support the RockRidge extensions which are used by the Ubuntu alternate iso for having 64+ characters in filenames. See https://bugs.launchpad.net/unetbootin/+bug/373089 and http://sourceforge.net/tracker/?func=detail&aid=2928072&group_id=14481&atid=114481 for the bug reports detailing the issues. Unfortunately this means that UNetbootin isn't going to be able to support Ubuntu alternate iso files, even with the magical "cdrom-detect/try-usb=true" option, until the bug is fixed in 7-zip.
@Andrew Henry: the issue is that some udeb files in the Ubuntu alternate iso have more than 64-character filenames, but unfortunately they are truncated to 64 characters (and hence can't be found by the installer) because 7-zip, which is used by UNetbootin for extracting iso files, doesn't support the RockRidge extensions which are used by the Ubuntu alternate iso for having 64+ characters in filenames. See https:/ /bugs.launchpad .net/unetbootin /+bug/373089 and http:// sourceforge. net/tracker/ ?func=detail& aid=2928072& group_id= 14481&atid= 114481 for the bug reports detailing the issues. Unfortunately this means that UNetbootin isn't going to be able to support Ubuntu alternate iso files, even with the magical "cdrom- detect/ try-usb= true" option, until the bug is fixed in 7-zip.