Cannot install an aboot boot block

[Stephane Bortzmeyer <stephane@transfer.ul.edu.lb>]

On an AlphaServer 1200, Debian woody runs fine but the machine needs
its floppy to boot. I installed the woody package of aboot and used it
to:

swriteboot -v /dev/sdc /boot/bootlx

It seems fine:

preserving boot partition 1
bootsize:165 sectors
bootsect:2
done!

but SRM claims:

failed to read dkb200.2.0.2.1
bootstrap failure

(I tried all the disks indicated by "show dev" in case I
misinterpreted the naming scheme. Only dkb0, where Digital Unix
resides, works.)

fdisk on /dev/sdc shows that the first cylinder is free. 

Detected an OSF/1 disklabel on /dev/sdc, entering disklabel mode.
To return to DOS partition table mode, use the 'r' command.

BSD disklabel command (m for help): p

3 partitions:
#       start       end      size     fstype   [fsize bsize   cpg]
  a:        2       900       899       ext2                    
  b:      901      1100       200       swap                    
  c:     1101      5038      3938       ext2