PHP VirtualBox Manager (Help) | NETGEAR Communities

The reason for this problem is that VirtualBox changed the auth system for connecting to VirtualMachines but didn’t reflect that change in vboxwebsrv. Thus, authentication will always fail unless a new Version of VitualBox fixes this.
For References see here: (vboxwebsrv authentication problem)

The only “solution” so far is to disable VirtualBox’s internal auth by doing

VBoxManage setproperty websrvauthlibrary null

Of course this will leave the barn door wide open, so you may want to play with .htaccess and friends like outlined here. (Authentication System)

-Stefan