OK, what I did:
I included the startup commands for the vbox interface into the script of my virtualbox launch. now the interface is startet, when i start the machine. Problem solved.
Thanks alot guys!
VBoxTunctl -u root -g vboxusers -t vbox0
ifconfig vbox0 up
brctl addif br0 vbox0
sudo -H -u vmuser VBoxManage startvm 10 --type headless