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)
Intel Core i7-14700K - 14th Gen 20-Core (8P+12E) LGA 1700 125W CPU Processor
$373.96
Intel Core i7 CPU Processors, I7 2600, i7 3770, i7 4770, i7 4790
$28.99
Intel Core i5-6500 6th GEN Quad-Core 3.2GHz FCLGA 1151 CPU Processor SR2L6
$23.99
Intel Core i7-3770 Desktop Processor (3.4 GHz, 4 Cores, LGA 1155) Ivy Bridge
$29.99
Intel - Core i5-14600K 14th Gen 14-Core 20-Thread - 4.0GHz (5.3GHz Turbo) Soc...
$305.99
10th GEN INTEL Core i5-10400F 2.9GHz Socket-1200 Desktop CPU SRH3D Processor
$69.99
Intel Core i7-4790K SR219 4.00GHZ 4Th Gen Used Desktop Processor CPU FCLGA1150
$64.99
SR1XP Intel Xeon E5-2680 v3 12 Core 30MB 2.5GHz LGA 2011-3 Grade A Processor
$3.87
Intel Core i7-13700KF - 13th Gen Raptor Lake 16-Core (8P+8E) Desktop CPU Proc...
$289.99
INTEL CORE I5-8600 PROCESSOR | 3.10GHZ | SR3X0
$59.99