new 6.1.4 fails to boot

[steve%prd.co.uk@localhost (Steve Blinkhorn)]

I am in the throes of replacing a number of systems with small
"nettop" devices.   Inevitably these come with MS-Windows
pre-installed, and in some cases the was this OS is
installed does not make ofr easy co-residency.   So I am installing
NetBSD no in an FDISK partition but overwriting the disk completely.

This has worked fine until today, when after foing through the
following installation procedure the system failed to boot.   (I
should say that things went fine with an exact duplicate using the
smae procedure).

I have a complet 6.1.4 system installed on a USB disk, with the 6.1.4
installation image file in the root directory.   I configure this as
vnd0a and mount on /mnt.   Then I cd to /mnt and run ./sysinst.
Everything seems to go fine (except for network configuration - I
imagine that is because the existing running kernel won't allow it.

But when I try to boot from the disk on which I have just installed
NetBSD, the boot loader fails to find hd0a:netbsd or any of the
fallback alternatives.

I have never, ever had problems installing NetBSD before so I'm not
very experienced booting manually.  'ls' just reports 'not found'.
If I mount hd0a having booted from the USB disk everything looks to be
in place, the file system fsck's as clean.

I don't know whether this is strictly and amd64 problem, and it feels
to me embarrassingly elementary.   Can anyone wuggest how I should
proceed?

-- 
Steve Blinkhorn <steve%prd.co.uk@localhost>