Failed to connect to the VirtualBox kernel service while enabling copy-paste

I am assuming you ran Insert Guest Additions CD Image from the VirtualBox menu and ran the disk in your VM.

I had a similar issue where my Bidirectional Clipboard was working and then stopped after an update. I was getting the error message displayed: vboxclient the virtualbox kernel service is not running. Reinserting the Insert Guest Additions CD Image and reinstalling the services FIXED my issue.

I am using VirtualBox ver. 5.0.20. with Fedora 23 VM.

I am using VirtualBox 5.0.6 and I got the same error after I updated my guest virtual machine. This solved it for me.

sudo /etc/init.d/vboxadd setup

Then I used sudo /usr/bin/VBoxClient --clipboard to enable clipboard and it worked.

If you are using VirtualBox pre 5.x, use this

sudo /etc/init.d/vboxdrv setup

Check this answer for the VirtualBox Ubuntu 14.04 - vboxclient the virtualbox kernel service is not running question.