vmlinuz-5.0.21-3-pve

Fresh install on Debian Buster, following this install guide, adapted to Buster. On reboot, I get this: Loading Linux 5.0.21-3-pve ... error: /boot/vmlinuz-5.0.21-3-pve has invalid signature. Loading initial ramdisk ... error: you need to load the kernel first. and will not boot using that...