Had the same error message installing Ubuntu 20.04.1. Following Alexei Lozovsky's advice above, I made my EFI partition the first partition on the disk, and also made it a primary partition as opposed to a Logical partition within an extended partition, and the installation completed successfully. (My disk is still MBR partitioned, but I am using UEFI).
Had the same error message installing Ubuntu 20.04.1. Following Alexei Lozovsky's advice above, I made my EFI partition the first partition on the disk, and also made it a primary partition as opposed to a Logical partition within an extended partition, and the installation completed successfully. (My disk is still MBR partitioned, but I am using UEFI).