This error indicates that your UEFI firmware has a bug that prevents the installation of the iSCSI boot firmware table (iBFT). Switch to booting in “legacy” BIOS mode rather than UEFI mode.

If you are unable to switch to “legacy” BIOS mode, then you will need to contact your UEFI firmware vendor for a fix.

You may also work around the bug in your UEFI firmware using the --no-describe option of the sanboot command. This will allow iPXE to boot from the SAN device. However, since the UEFI firmware bug prevents iPXE from installing the iBFT, the booted OS will not be able to automatically locate the iSCSI disk.