In some cases when attempting to add a Hyper-V host in VM Backup you might get an error message saying that it's unable to add the host, specifically: "Failed to configure Hyper-V Host Agent."
Upon attempting to install the VM Backup Hyper-V Host Agent manually you get an error saying:
"The Windows Installer Service could not be accessed. This can occur if you are running Windows in safe mode, or if the Windows Installer is not correctly installed. Contact your support personnel for assistance."
This error usually happens on machines running Server Core since the feature 'WoW64 Support' is not installed automatically.
Run the command 'Get-WindowsFeature' through PowerShell whereby you should see the following feature marked as 'Available':
Next, run 'Install-WindowsFeature WoW64-Support' in order to install this feature. Once installed, reboot the machine and try adding the host in question again.