VirtualBox fails to start machine after installing extensions

I just added extension pack and my Windows machines won't start. This is the error I get:

Failed to open a session for the virtual machine Windoze 7.

The device helper structure version has changed.

If you have upgraded VirtualBox recently, please make sure you have terminated all VMs and upgraded any extension packs. If this error persists, try re-installing VirtualBox. (VERR_PDM_DEVHLPR3_VERSION_MISMATCH).

Result Code: NS_ERROR_FAILURE (0x80004005) Component: Console
Interface: IConsole {db7ab4ca-2a3f-4183-9243-c1208da92392}

I really don't want to re-install VB all over again, so I am hoping to find another solution. I tried some of the other suggested solutions but they didn't work for me. How can I fix this?

Solution 1:

THE RIGHT WAY

Yes, other answers are right: you have a extension-virtualbox mismatch. However, there is a better way, a more Ubuntu way, to solve this using the distro's own installer which is packaged as virtualbox-ext-pack and found in the multiverse.

1. If the multiverse is not enabled, enable the multiverse.
2. Close out of VirtualBox.
3. In the terminal, run sudo apt-get install virtualbox-ext-pack

if for any reason that's already installed and you want to have reinstalled (thus guaranteeing you fix all the problem).

sudo apt-get --reinstall install virtualbox-ext-pack

Solution 2:

The version of extension-pack MUST match the VirtualBox version.

You can do this easily in Ubuntu by running:

sudo apt-get --reinstall install virtualbox-ext-pack

If this still does not fix your issue, you can manually install the matching VirtualBox extenstion, by following the below instructions:

1. Download the latest .deb file for Ubuntu from here:
   https://www.virtualbox.org/wiki/Linux_Downloads

2. Double click on the downloaded .deb file. It will bring-up Software Centre.

3. Click on the Upgrade button to install the latest version.