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Since syslinux 6.xx is a major change from syslinux 4.xx versions, it is obvious it is failing to boot. Therefore you have a version mismatch and syslinux fails to boot. I guess the USB creators include syslinux 4.xx version (mostly 4.06 or 4.07) and the Arch iso contains files from syslinux 6.xx (either 6.01 or 6.02).
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The "Bootable USB Creators" programs in Windows typically include their own copy of syslinux which they use to install the MBR and ldlinux.sys (stages 1 and 2) but simply copy the *.c32 files available in the ISO, they do not overwrite the *.c32 files already present in the iso with the *.c32 files from their own copy of syslinux. 6.00 and 6.02 (which is the latest release ATM). Sometimes you will get boot failure when you mix even files from different minor versions, eg. You should not mix files from different syslinux versions. No, I meant, the MBR code (syslinux stage 1), ldlinux.sys (syslinux stage 2, installed by "extlinux" command) and the *.c32 files (syslinux modules) should be from the same syslinux version.
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Would that mean that if I use a different media, e.g. This error is because you are trying to use syslinux v6 *.c32 files (used by Arch) from syslinux v4 (currently installed in the USB).
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