Invalid boot signature

[Sven Garbade <garbade@psy.uni-muenchen.de>]

Hi all,

today I've deleted all Windows/DOS stuff on one of our Debian (Potato)
Boxes. Then I rearranged the hard disk. I know looks like:
                                                      size in MB
 hda1        Boot        Primary   Linux ext2         789.63
 hda5                    Logical   Linux              2097.45
 hda6                    Logical   Linux              2097.45
 hda7                    Logical   Linux ext2         16.46
 hda8                    Logical   Linux swap         131.61
 hda9                    Logical   Linux              5124.35

When I run lilo, I got this error message:

$:/sbin/lilo 
Added j
Added n
Added r *
Fatal: First sector of /dev/hda1 doesn't have a valid boot signature

What does this means?
There are no problems while booting, the system runs fine. But I can't
reconfigure lilo. 

Thanks, Sven