As part of my ongoing experiment to upgrade the Fedora Core image to version 4, I (backed up and) erased my current disks.

After creating a new Fedora Core 2 disk, I checked the configuration page, and the kernel selected was as expected the domU kernel.

But trying to boot it gave me: "This isn't a Xen kernel! Fix your configuration profile."

Going to the configuration page, selecting the Finnix kernel, saving, going there again, selecting the domU kernel, saving, fixed the problem.