After I reboot one of my VirtualBox host servers today, I was unable to start the virtual box guests. The error was a popular one: NS_ERROR_FAILURE.

The problem was caused by the kernel mismatch problem. All you need is to rebuild the virtual box library to match with your system kernel. In my case, I had the following:

#This is my Virtual Box version
6.0.16


#This is my Linux kernel:
uname -a
3.10.0-1062.12.1.el7.x86_64


#This is my virtual box modules version:
modinfo vboxdrv
filename:       /lib/modules/3.10.0-514.10.2.el7.x86_64/weak-updates/vboxdrv.ko.xz
version:        5.0.40 r115130 (0x00240000)
license:        GPL
description:    Oracle VM VirtualBox Support Driver
author:         Oracle Corporation
retpoline:      Y
rhelversion:    7.6
srcversion:     3AFDBBC6FDA2CE8CF253D33
depends:
vermagic:       3.10.0-957.1.3.el7.x86_64 SMP mod_unload modversions
parm:           force_async_tsc:force the asynchronous TSC mode (int)

As you can see, the Virtual Box kernel is loaded from a wrong kernel location. Also the Virtual Box is 5.0.40 instead of 6.0.16. In my case, all I need is to rebuild the virtual box library to make it compatible with the Linux kernel. In order to do it, you will need to do the following:

1. Remove all the old Linux kernels
2. Remove the Virtual Box modules.
3. Uninstall the Virtual Box
4. Reboot
5. Install the Virtual Box

#Remove all of the old kernels:
sudo package-cleanup --oldkernels --count=1 -y; 


#Remove all except your current modules:
cd /lib/modules/


#Uninstall the Virtual Box
sudo yum remove VirtualBox-6.0


#Reboot
sudo reboot


#Install the Virtual Box
sudo yum install -y VirtualBox-6.0


#Install the Extension Pack (The version number may be different in your case)
wget --no-check-certificate https://download.virtualbox.org/virtualbox/6.0.16/Oracle_VM_VirtualBox_Extension_Pack-6.0.16.vbox-extpack
sudo VBoxManage extpack install --replace Oracle_VM_VirtualBox_Extension_Pack-6.0.16.vbox-extpack


#Start the Virtual Box again

That’s it! Hope it helps!