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)
Dell Optiplex 7060 SFF 8th Gen Core i7 3.2GHZ 32GB 512GB Win 11 Pro
$249.00
Dell Precision 3420 SFF Intel Core i5-6500 8GB RAM 256GB SSD WIN 11
$75.00
HP Z820 8-Core 2.60GHz E5-2670 128GB RAM No HDD No OS
$235.90
HP Chromebase Desktop PC 21.5" FHD Core i3-10110U Intel UHD 8GB DDR4 128GB SSD
$359.99
Intel - Core i9-13900K 13th Gen 24 cores 8 P-cores + 16 E-cores 36M Cache, 3 ...
$689.99
Intel - Core i7-13700K 13th Gen 16 cores 8 P-cores + 8 E-cores 30M Cache, 3.4...
$489.99
AMD Ryzen 9 5950X 16-core 32-thread Desktop Processor
$319.99
Intel - Core i9-12900K Desktop Processor 16 (8P+8E) Cores up to 5.2 GHz Unloc...
$619.99
New HP S01 Slim Desktop PC & 27" Monitor 12th Gen Core i3 4.30ghz 8GB 512GB SSD
$319.99
SGIN 17.3 inch Laptop 8GB RAM 512GB SSD IPS 1080*1920 HD Intel Quad Core 2.9 GHz
$259.00