Encountered the same problem using expert mode install with 9.10 Server Edition (ubuntu-9.10-server-amd64.iso).
The following workaround, immediately prior to running the GRUB install step, solved the problem.
- open shell - mkdir /boot - mount -t ext2 /dev/sda5 /boot - cp /etc/mtab /target/etc/mtab
GRUB installed cleanly and the system rebooted without issue.
Encountered the same problem using expert mode install with 9.10 Server Edition (ubuntu- 9.10-server- amd64.iso) .
The following workaround, immediately prior to running the GRUB install step, solved the problem.
- open shell
- mkdir /boot
- mount -t ext2 /dev/sda5 /boot
- cp /etc/mtab /target/etc/mtab
GRUB installed cleanly and the system rebooted without issue.