kldload: can't load /boot/modules/vboxdrv.ko: Exec format error

On FreeBSD 10.0-CURRENT #1 r238671: Sat Jul 21 16:21:32 CEST 2012
(/usr/src recently update, is at Revision: 238672), VirtualBox seems to
be broken:

kldload: can't load /boot/modules/vboxdrv.ko: Exec format error

When both buildworld and kernel as well as /usr/src itself were at
Revision: 238671, I did a build of the whole port
/emulators/virtual-box-ose[-kmod] to prevent the vboxdrv.ko kernel
module located in /boot/modules/ and its siblings being in sync with
/usr/src.

But it doesn't work. I searched the net and I only found hints of the
form that both, /usr/src and the last time the module
/emulators/virtual-box-ose-kmod has been build are out of sync. This is
not the case in my case.

VirtualBox is at version 4.1.18.

What is wrong? Am I wrong and repeating an error over and over again?

Regards,
Oliver