Please, please can I get some help, before I tear out my remaining hair!!!
I had VB working, but I screwed it up, decided to re-install, now the "Machine and Devices" menus are grayed out, making it impossible to add Guest additions. Ubuntu 10.10 64 bit host/guest Win XP.
I have re-installed the download to get version 4.
Could someone please give me some simple advice as to what I need to do?

I looked at this yesterday and decided that I probably didn't know enough about Virtual Box to answer (I've been experimenting with it for the past month or so but I'm still learning).

But I'll dive in with a suggestion:

1. With Virtual Box shut down, rename your dot-virtualbox directory (I usually go with appending "dot bak" in cases like these).

2. Start Virtual Box and test. It should create a new dot-virtualbox directory.

If the problem goes away, something in the dot-virtualbox directory is likely corrupted. If it were me, I would then
a. Shutdown VB and create a backup copy of the new dot-virtualbox directory (dot-virtualbox.clean).

b. Replace elements in the new working dot virtualbox directory with elements from the old one ONE AT A TIME, removing each element after each test, to identify if a particular one were to blame.

3. If that does not work, I would use Synaptic to do a complete removal (remember, I already have a copy of the dot-virtualbox directory) and reinstall and test again.

Take notes so you can remember what you did and don't end up duplicating effort.

Testing one thing at a time is tedious, but it works.

Hope you selected the right Guest OS in the Virtual Machine Wizard or VM Settings. If that doesn't work, you can always manually download the Guest Additions ISO and mount it as a CD drive in the VM to get your job done.

After a great deal of searching I did find an answer.
The first copy I downloaded from the VB site (the PUEL version) then I ran into problems, and not knowing any different reinstalled from the repositories (the OSE version). This didn't remove all of the original files, leaving behind a reduced and grayed out 'Devices' menu.
I finally, because of problems with the original install of Mint, did a complete wipe and install. Now works fine!
On another note.
If installing into a Hardware Raid 1 array, ignore most if not all of the instructions on the web. All that information is totally wrong!! I have just installed a 64 bit Mint 10.10 from the live DVD, without having to use an 'alternative' disc as advised by the web. That information is strictly for software Raid, but it doesn't make that clear at all. We should publish this information as it totally screwed me up on my install, over a week of wasted effort.