We have recently observed that the latest build of VirtualBox i.e. version 6.1 is having some compatibility issue with the Vagrant and a lot of our users are running into an error while setting up their virtual environment.
If in case you have downloaded the version 6.1 then please uninstall it and download the VirtualBox version 6.0.14 using this link.
[Edit :] Please restart your system after fresh installation.
Please feel free to get back to us if you have any query.
Curriculum Services Engineer