I'm not that familiar with VirtualBox so I'm going with the solutions proposed in these two threads (I recommend reading through the second one as it has some more interesting details about it).
On the terminal, disable the kernel module responsible for KVM (Kernel-based Virtual Machine) as it seems to conflict with VirtualBox. This likely means that you cannot run both VirtualBox and KVM at the same time, unless until you re-enable the module:
# If you are using an Intel CPU
sudo modprobe -r kvm_intel
# If you are using an AMD CPU
sudo modprobe -r kvm_amd
Test if this works first, as this command will only last until your next reboot. If this works and want to make the change permanent, you can create a new entry in /etc/modprobe.d/blacklist.conf:
blacklist kvm_intel