Virtualbox: the VirtualBox kernel service is not running. Exiting

 Had this very error and tried numerous approaches to resolve including upgrading and downgrading the kernel installing devel kernels etc. etc. but the below worked for me straight away -

sudo vi /etc/X11/Xsession.d/98vboxadd-xclient
Then you need to find the line with notify-send "VBoxClient: the VirtualBox kernel service is not running. Exiting."
For me I changed notify-send to echo so it looks like this
echo "VBoxClient: the VirtualBox kernel service is not running. Exiting."

Restarted and no error message - Thank God! this was so annoying 

https://forums.virtualbox.org/viewtopic.php?t=74366#:~:text=Re%3A%20VBoxClient%3A%20The%20virtualbox%20kernel%20service%20is%20not%20running&text=You%20have%20two%20choices.,install%20or%20install%20them%20again.