I wrote an .img file containing a custom debian distro to a USB stick via win32diskimager program. The stick doesn't boot on my older motherboard, returning:SYSLINUX: No DEFAULT or UI configuration directive foundI learned that it's because my motherboard doesn't recognize FAT32 partitions. It will only boot from a FAT16 partition. Sadly win32diskimager creates a FAT32 partition by default and there are no means to configure it.I found a workaround by someone who wrote: I've managed to recreate with fat16 filesystem, by reformatting the  525MB partition, copying over the files and reinstalling syslinux  (latest version, 4.05) - and now it boots. It looks like indeed some  motherboards have issues booting from fat32 USB sticks.I have followed the workaround and done this:Made a copy of all the contents of the fat32 partitionUnmounted and formatted the fat32 partition to fat16 via gparted (at this point the new fat16 partition is not marked as boot in the flags column)Copied the contents back to the newly created fat16 partitionUnfortunately I do not know how to reinstall syslinux on the USB stick so that it boots. I've got syslinux available (syslinux --version => 4.05) from the command line but have no idea what to do with it.
How to re-install syslinux on a re-formatted (fat32 to fat16) partition
debian;usb drive;live usb;syslinux
Check that you USB fat16 partition is still /dev/sdb1.Open a terminal window (Ctrl+Alt+T).Execute this command:$ sudo syslinux --directory /syslinux/ --install /dev/sdb1