VirtualBox guest additions installation issues

[Norbert Beckmann]

FreeBSD 9.1 as guest in VirtualBox 4.2.16 (on Solaris 11.1 x86):
Unable to install the guest additions.

Just did a portsnap fetch update.
Then trying to install the guest additions, i.e.
# cd /usr/ports/emulators/virtualbox-ose-additions
# make install clean
===>  Installing for virtualbox-ose-additions-4.2.16
and so on ...,
finally installation stops with the following message:

install  -o root -g wheel -m 555 
/usr/ports/emulators/virtualbox-ose-additions/work/VirtualBox-4.2.16/out/freebsd.amd64/debug/bin/additions/vboxvideo.ko.symbols 
/boot/modules
install: 
/usr/ports/emulators/virtualbox-ose-additions/work/VirtualBox-4.2.16/out/freebsd.amd64/debug/bin/additions/vboxvideo.ko.symbols: 
No such file or directory
*** [do-install] Error code 71

Stop in /usr/ports/emulators/virtualbox-ose-additions.
*** [install] Error code 1


How can I work around these missing "vboxvideo.ko.symbols"?

Thanks

Norbert