This evening I ran into this error while installing Ubuntu 21.04.
I upgraded from 20.04 by formatting the existing ext4 partition.
My BIOS is set to Legacy mode.
Then suddenly I got this error and that ended the installation.
I tried again, but same error message.
Then I read about the efi partition, so I removed it. After that I could finally install the new system.
This evening I ran into this error while installing Ubuntu 21.04.
I upgraded from 20.04 by formatting the existing ext4 partition.
My BIOS is set to Legacy mode.
Then suddenly I got this error and that ended the installation.
I tried again, but same error message.
Then I read about the efi partition, so I removed it. After that I could finally install the new system.