I prefer to have VBox manager open so I can either run the VM from VBox manager (as r/o) or VMUB (as rd/wr) - however I get more problems with VBox mgr open.
Well, if the autodetect method finds the VB Manager open it will "switch" internally to using VBoxManage.exe. If it will not find it, it will "switch" to updating directly, solving your problem.
The detection code is checking every time you click on the Start button, so it will adapt if you close or restart VB Manager.
Give it a try...
Also, the .vmdk shows up as inaccessible in VBox mgr (as in the video) unless I login as user=admin so I can't run the VM from VBox in this mode.
A normal user can't access a real drive directly. That's why VB and VMUB have to be started as an administrator.
Unfortunately I can't change this because Windows is made this way.
BTW, Linux is even "worst" with this