install/52441: install netbsd 7.1 bootable error

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>Number:         52441
>Category:       install
>Synopsis:       install netbsd 7.1 bootable error
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    install-manager
>State:          open
>Class:          support
>Submitter-Id:   net
>Arrival-Date:   Sun Jul 30 07:20:00 +0000 2017
>Originator:     Michail
>Release:        netbsd 7.1 notebook
>Organization:
reslab
>Environment:
no install OS, img x86
>Description:
install OS netbsd 7.1, error write boot 
> installboot: Old BPB too big, use -f (may invalidate filesystem)
> installboot: Set bootstrap operation failed

i'm exit install:
> # installboot -f -o console=pc,speed=9600 /dev/rwd0a /usr/mdec/bootxx_ffsv2

result:

>NetBSD MBR boot
>NetBSD/x86 ffsv2 primary Bootstrap
>Boot failed (errno 2): cant open /boot
>Operation System not found

please help install
>How-To-Repeat:

>Fix: