virtualbox.org

I downloaded VirtualBox 6.0.4 and I downloaded the latest extension pack. This is the error I get when I try to install it:
This is in the Details window
I was searching around and found some people getting an error similar to mine, but the problem was that they were installing an Extension pack that was incompatible with the version of VirtualBox they had. In my case both the Extension Pack file and VirtualBox deb file that I downloaded both say "6.0.4" on it, indicating that they should be compatible. The strange thing, however, is in VirtualBox when I go to Help > About VirtualBox I see that it says

VirtualBox Graphical User Interface Version 5.2.18_Ubuntu r123745

It says 5.2.18. How can that be?

Update. It turns out the two were incompatible. I was able to solve this by searching for the correct extension pack. I went to Googled "virtualbox 5.2.18 extension pack" went to the first link, scrolled down to VirtualBox 5.2.18 and selected the Extension Pack.

dgodfrey wrote:VirtualBox Graphical User Interface Version 5.2.18_Ubuntu r123745

This is the Ubuntu tribute band version of VirtualBox (a.k.a. a fork). This is something that you will have installed directly from the Ubuntu repos. v5.2.18 is getting a bit old now so the recommendation would be to purge that and install either v5.2.26 or v6.0.4 from the official VirtualBox repo and install the matching ExtPack.

-Andy.

The extension pack and the Guest Additions are completely independant features.

It's very simple: the extension pack is a plugin pack for the host. It extends the feature set of VirtualBox itself and affects all VMs at once.

The Guest Additions - and the name is a bloody big clue here - is a bunch of drivers etc which you install in each guest to improve co-operation with the host software. You have the guest additions from the 5.2.18 Ubuntu VBox fork installed.

Since these are installed separately - by users - there is every reason to expect that their versions will diverge, or even be for the wrong software entirely.