Guest Additions 'unable to insert the virtual optical disk' Ubuntu 16.04

[GOG!]

Hello!

I am unable to install Guest Additions! Creating a VM is no problem and all I want to achieve is to put a USB memory stick in the host and use it in the guest but whenever I click on 'Insert Guest Additions CD image...' I get a VirtualBox error pop-up 'Could not mount the media/drive '/usr/share/virtualbox/VBoxGuestAdditions.iso' (VERR_PDM_MEDIA_LOCKED).

I've been trying to install GuestAdditions by following the instructions given on this page - (well, it seems I've not been a member long enough to post urls but it was on virtualboxes site) but run into the above problem at step 7.

I'm not suggesting it's a problem with anything other than this user (me) but I have absolutely no idea what I've either done wrong or haven't done and I certainly have no clue as to what to do next! Help in the form of an idiot-proof, dummies guide would be most appreciated.

Host - Ubuntu 16.04 LTS (and user added to 'vboxusers' group)
Guest - Ubuntu 16.04 LTS
VirtualBox 5.2.10 and VBoxGuestAdditions_5.2.10

Tim

[ChipMcK]

there is already a CD/DVD in the optical drive.

1. Eject cd/dvd already in optical drive.
2. Insert the GAs iso.
3. Run GAs
4. Once installed, EJECT the iso From the optical Drive

[GOG!]

Thanks for prompt reply.

OK. So I'd already done that step but didn't find result at all intuitive - I couldn't notice anything different so assumed I'd done something wrong!

However, following your instructions and having re-installed Guest Additions I had another look at the settings and now, when clicking 'usb device filters>add' I'm presented with a list of all devices attached to the host (I wasn't before) - perfect, thank you!

But that begs another question. It seems I have to shut down the guest machine in order to use the device back in the host machine. Is there a way to 'switch' which machine currently can use the device while the guest is running? Or am I asking too much?

Tim

[ChipMcK]

It seems I have to shut down the guest machine in order to use the device back in the host machine. Is there a way to 'switch' which machine currently can use the device while the guest is running? Or am I asking too much?

depends on what device you are referring to.

it is difficult to read minds across/over a forum.

[GOG!]

Point taken - as the question asker it was obvious to me what I was talking about! Just a simple USB memory stick. If shutting down the guest is the way it works then fine - just wanted to make sure I'm not missing somethng (I'm finding it harder these days to retain all the info I read).

[ChipMcK]

A USB may be online to one system at any given time
OR
offline to all systems.

1. Eject from one system (guest or host)
2. Mount on another system (guest 2 or host)

Usage of USB filters greatly facilitates 'flipping' between systems.
Refer to USB basics and troubleshooting