"Failed to Create VirtualBox Client.com " error on launch

[AlWilcox]

After a system reboot, I can no longer launch VB. It errors out with the following:

Failed to create the VirtualBoxClient COM object.
The application will now terminate.
Document is empty.
Location: '/home/al/.config/VirtualBox/VirtualBox.xml', line 1 (0), column 1.
/build/virtualbox-Xs7cR9/virtualbox-5.0.24-dfsg/src/VBox/Main/src-server/VirtualBoxImpl.cpp[534] (nsresult VirtualBox::init()).
Result Code: NS_ERROR_FAILURE (0x80004005)
Component: VirtualBoxWrap
Interface: IVirtualBox {0169423f-46b4-cde9-91af-1e9d5b6cd945}

Ubuntu 16.04 LTS

How do I troubleshoot from here?

[mpack]

Is the document really empty? What is the contents of ''/home/al/.config/VirtualBox/VirtualBox.xml'?

Did you do anything to the host recently, such as create a new user account?

Also a VM log wouldn't go amiss. Any affected VM will do. You can find a log in the "Logs" subfolder of the VM folder. Compress "VBox.log" (ONLY) to a zip file. Attach the zip here.

[AlWilcox]

The .VBOX file is empty. It is a Windows 10 session, so that is the name of the .VBOX file. There is a Windows 10.VBOX-Prev file, which does have XML code. I tried renaming the empty file, and copying Prev file to Windows 10.VBOX. When I try to run it, I get the same error message. When renamed, the file does change to a VBox icon.
Did not do anything lately except apply system updates, which required a reboot. Before rebooting, I ended my VM session normally, shut down any open programs, then rebooted. That's when it occurred. Strange!
Windows 10. is the only session I run on VM, since my OS is Linux 16.04 LTS, and I have some software that only runs on Windows. Nice solution until this occurred.

[mpack]

Uh.. your first post discussed VirtualBox.xml, it did not discuss any .vbox file. If the former is empty then it needs to be repaired in the same way you recovered the .vbox file, or from your most recent backup.

Oops. The log shows you aren't running VirtualBox after all, so we can't support you here. You're running the Ubuntu fork of the source code. If you install VirtualBox then we can help you here (if you still have a problem), otherwise you need to go to the Ubuntu forums.

[AlWilcox]

OK. Thanks. Will give Ubuntu a shot. I thought this was the support forum for the VM software.