Comment 32 for bug 732149

If you are unable to boot as a result of similar symptoms as was seen in this bug (which should be fixed by now, presumably, comment/report new if not) there is a possible workaround to enable booting after the grub config file has been written whilst grub-probe is unable to detect the btrfs:

1. At the boot menu [e]dit the entry and look at the kernel line:
linux /vmlinuz-2.6.38-8-generic root=/dev/mapper/mellu-uburooot ro rootflags=subvol=@ quiet splash vt.handoff=7

3. IF the "rootflags=subvol=@" boot option is missing add it, and then boot the command list using ctrl+x

4. Once booted make sure that grub-probe detects the btrfs OK and then run update-grub.