I've had the same issue in the past.
Apparently the vboxweb-service was sometimes starting too early before other necessary services were running.
For me, the following workaround did the trick.
I changed the startup depedencies of the vboxweb-service:
edit "Required-Start" value in the vboxweb-service init.d file:
Change this (not sure what it was before. Probably vboxdrv) :
$all makes sure that the service is started after all the other services are started.
Hit Ctrl + X and save the file.
Afterwards run this command:
regards,
mo