This message occurring during boot up of KNOPPIX-Live has no deleterious consequences but it is an annoyance.
It is probably an unintended hangover from the HD-installed version which allocates several partitions.
Either ignore it or include a (2nd and) 3rd (and 4th) partition in your boot device, even if it is a USB stick.
Use fdisk* to set /dev/{sda}1 as the KNOPPIX partition type c (being FAT32; or NTFS if you prefer - I've never tried this).
Set /dev/{sda}3 as type 83 (Linux) (at least 400M). Then format it as Reiserfs with mkreiserfs .
It's not obvious to me how (or even whether) the partition is used; but it is made available; and you will boot
without the annoying error message!
(*) Yes: you need to format your intended USB device - from a temporary KNOPPIX USB device is probably your most
convenient method ;o)
$599.99
CISCO MCS 7800 (2x) Intel Xeon @ 2.33 GHz 4GB Ram, NO HDD
$44.99
$80.00
Dell PowerEdge R720 Server - 2x8c CPU,256Gb RAM, 128Gb SSD/3x900Gb SAS, Proxmox
$340.00
Intel Xeon Gold 6126 2.6 GHz LGA 3647 Server CPU Processor SR3B3
$17.99
Intel Xeon E5-2680 v4 2.4GHz 35MB 14-Core 120W LGA2011-3 SR2N7
$17.99
Intel Xeon Gold 6140 SR3AX 2.3GHz 18-Core Processor CPU
$44.99
Intel Xeon Gold 6138 2.0GHz 27.5MB 20-Core 125W LGA3647 SR3B5
$46.00
INTEL XEON GOLD 6148 PROCESSOR | 2.40GHZ | SR3B6
$99.99
HP Workstation Z640 2x Xeon E5-2623V4 32GB Ram Dual 256GB SSD K420 Linux GA
$234.98