USB multiboot support for Kali dropped !?

[qwik]

I have a multiboot FAT32 USB with Kali, other LiveCD's and data. It was working fine until I tried to update. The last I used was the kali-linux-2016-W36-amd64.iso and want to update to kali-linux-2016-W49-amd64.iso. Now there are problems booting. Does this have anything to do with a kernel rewrite?

The official way still works, dd to USB, but that is not user friendly with a 32GB USB and all my other stuff
I get the error "IO charset ascii not found, mounting root file system failed", when booting from USB.
I get no error, but only X-mouse on black background in graphic mode and no desktop, when booting the ISO file from USB in virtualbox.

If you want to recreate my errors:
-use 4+ GB FAT32 USB
-extract the "live" folder to USB
-extract the "isolinux" folder and put inside the live folder
-rename isolinux.cfg to syslinux.cfg
-get syslinux.exe 6.03 [for windows]
-run "syslinux MBR.cmd"

@echo off
set DISK=%~d0
IF %DISK%==%systemdrive% goto end
IF %DISK%==\\ goto end
set MAP=%~dp0
echo Installing Syslinux MBR on drive %DISK%
"%MAP%syslinux.exe" --version
pause
"%MAP%syslinux.exe" -m -a -d /live/isolinux/ %DISK% 
attrib -s -h %DISK%\live\isolinux\ldlinux.sys
attrib -s -h %DISK%\live\isolinux\ldlinux.c32
echo done!
pause
:end

On my multiboot USB I use a menu to choose the different LiveCD's, and all others boot just fine. The booting of Kali works until the squashfs is loaded.
USB boot mounting.jpg
ISO boot mounting.jpg