I have a Linux VM on a Windows 7 host. I've configured it to enable VRDP on port 6000 with the appropriate VBoxManage modifyvm commands. However, when I start the virtual machine with VBoxHeadless --startvm, it just sits there at the copyright notice. I never get any notification that the VRDP server has started, nor can I connect to localhost:6000 using the Windows Remote Desktop client. I've opened TCP port 6000 in Windows Firewall, so I don't think it's a firewall issue. Is there anything else I need to do to get VirtualBox's VRDP server to start?
As it turns out, I didn't have the VirtualBox extension pack installed. For some reason the VirtualBox documentation doesn't mention that you need the extension pack in order to run the VRDE server on Windows.
The Linux version (or at least, the version included in most Linux package repositories) appears to have this component by default, so I wasn't expecting it to be missing on Windows.