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)
$3200.00
Vintage Atari 1040STf Computer with Mouse and Box, Minimal Testing, Pls Read
$149.99
ATARI 4 Meg STACY ST (For Parts)
$500.00
Atari Power Cube 800XL, 600XL, 65XE, 130XE USB-C Power Supply PSU
$11.25
A8picoCart Atari 130 / 65 XE 800 / 1200 XL XEGS multicart UnoCart clone game
$32.95
Atari 400/800/XL/XE Computer SIO2PC - PC/Mac Disk Drive Emulator Adapter/Device
$15.25
Rare Vintage Collectible Original Atari 800 Home Computer With Case - UNTESTED
$219.99
Atari 600 XL Vintage Home Computer Unused, CiB See Description For Details
$199.99
ATARI Home Computers HOME FILING MANAGER Software **SEALED NEW** 1982
$25.00
TEAM TAP Atari Jaguar Multi Player Adapter NEW In Box
$25.46