I tried to burn a Linux ISO to a bootable USB disk, and while booting the disk, it failed with the below error message:
Failed to load COM32 file menu.c32
Apparently this is due to a recent change in syslinux library modules. Not sure if its a bug Unetbootin can fix or any other package related bug.
But the solution is simple.
copy the below files from /usr/lib/
If the above files were not enough and if you are getting the below message as Taipan in comments observed,
Failed to load COM32 file vesamenu.c32
copy /usr/lib/syslinux/vesamenu.c32 as well to the root of USB device and try again.
Hope this works. Source of the above solution is here.
Commenter Fabien has noted his location of the above files was as shown below