> Rebooting with command : netbsd.GENERIC -s
> Boot device: /sbus/esp@0,800000/sd@0,0   File and args: netbsd.GENERIC -s
> >> NetBSD/sparc Secondary Boot, Revision 1.8
> >> (pk@flambard, Sat May  8 21:54:06 MEST 1999)
> Booting netbsd.GENERIC @ 0x4000
> Bad format
> Program terminated

You are using a boot program (note the date) that does not know how
to load ELF kernels.

> Now, I can still boot up with 19990620 boot-floppy to access the disk but I 
> don't really know how to fix this.

There is no `19990620 boot-floppy' -- at least not in the snapshot
that I uploaded -- so I suspect you are using the 1.4 release image
which also explains the installation of the older boot program.

Since you can go to single-user from a network boot, you can:

	mount /dev/sd0a /mnt
	cd /usr/mdec; ./binstall ffs /mnt

assuming `/usr/mdec' contents from the latest snapshot. If the latter
isn't the case, I suggest you copy the snapshot's miniroot image
to `/dev/rsd0b', boot it and fix up the boot program from there
(see also the install docs for details).

-pk