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)
SGIN 17.3" Laptop 8GB RAM 512GB SSD Notebook with IPS Full HD 2.8GHz Windows 11
$269.00
A-Tech 8GB DDR3 1600 PC3-12800 Laptop SODIMM 204-Pin Memory RAM PC3L DDR3L 1x 8G
$13.99
Team T-FORCE VULCAN Z 16GB (2 x 8GB) 288-Pin PC RAM DDR4 3200 (PC4 25600) XMP
$35.99
HyperX FURY DDR3 8GB 16GB 32GB 1600 MHz PC3-12800 Desktop RAM Memory DIMM 240pin
$12.90
Crucial 16GB (2x 8GB) Kit DDR3L 1600MHz PC3-12800 UDIMM Desktop 240-Pin CL11 RAM
$23.33
Crucial DDR3L 16GB 1600 2x 8GB PC3-12800 Laptop SODIMM Memory RAM PC3 16G DDR3
$21.50
G.Skill RipJaws V 16GB (2x8GB) PC4-28800 (DDR4-3600) Memory F4-3600C16D-16GVKC
$23.50
Samsung 8 GB PC4-17000 DDR4-2133 1Rx8 DDR4 Desktop Memory HP P/N 798034-001
$10.00
HyperX FURY DDR4 16GB 32GB 64GB 2666MHz PC4-21300 Desktop RAM Memory DIMM 288Pin
$119.80
A-Tech 64GB Kit 2x 32GB PC4-25600 Laptop SODIMM DDR4 3200 MHz 260-Pin Memory RAM
$123.99