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I tried to create a USB rescue device using Backupper 4.0.6 under Windows 8.1 x64. I tried WinPE with UEFI, WinPE with legacy, and the Linux option, but none of them produced a bootable USB drive. I tried booting the USB drive on three different PCs; all failed. On my main (desktop) PC, it indicated that it was an attempted ISOLinux boot each time, even when booting the WinPE device. The other two failed to boot with a generic BIOS error message.
I then tried the export to ISO option, and then used Rufus to write that to the USB drive. It worked perfectly, and I was then able to do the restore I was trying to do without any more issues.
Since I did get the USB written, I don't need any help with this now, but if it is a bug in Backupper, you should know about it so you can take care of it.