VirtualBox 6.1.0 has been released. Unfortunately, Vagrant 2.2.6 doesn't work with this new release. This isn't an issue with this repository, but it may affect people using these boxes. It should be fixed in the next release of Vagrant (see hashicorp/vagrant#11249), but here's how to work around the problem in the meantime.

Credits:

• @scoter-oracle blogged about a very similar issue last year.
• @briancain has developed a fix for the next Vagrant release (see briancain/vagrant@fb4e698)

The workaround requires 3 changes.

First, in the file /opt/vagrant/embedded/gems/2.2.6/gems/vagrant-2.2.6/plugins/providers/virtualbox/plugin.rb, add a line at the end of the Driver module for VirtualBox 6.1, as follows. (On Windows, the file location is C:\HashiCorp\Vagrant\embedded\gems\2.2.6\gems\vagrant-2.2.6\plugins\providers\virtualbox\plugin.rb.)

module Driver
  autoload :Meta, File.expand_path("../driver/meta", __FILE__)
  autoload :Version_4_0, File.expand_path("../driver/version_4_0", __FILE__)
  autoload :Version_4_1, File.expand_path("../driver/version_4_1", __FILE__)
  autoload :Version_4_2, File.expand_path("../driver/version_4_2", __FILE__)
  autoload :Version_4_3, File.expand_path("../driver/version_4_3", __FILE__)
  autoload :Version_5_0, File.expand_path("../driver/version_5_0", __FILE__)
  autoload :Version_5_1, File.expand_path("../driver/version_5_1", __FILE__)
  autoload :Version_5_2, File.expand_path("../driver/version_5_2", __FILE__)
  autoload :Version_6_0, File.expand_path("../driver/version_6_0", __FILE__)
  autoload :Version_6_1, File.expand_path("../driver/version_6_1", __FILE__)
end

Second, in the file /opt/vagrant/embedded/gems/2.2.6/gems/vagrant-2.2.6/plugins/providers/virtualbox/driver/meta.rb, add a line at the end of the driver_map section for VirtualBox 6.1, as follows. (On Windows, the file location is C:\HashiCorp\Vagrant\embedded\gems\2.2.6\gems\vagrant-2.2.6\plugins\providers\virtualbox\driver\meta.rb.)

driver_map   = {
  "4.0" => Version_4_0,
  "4.1" => Version_4_1,
  "4.2" => Version_4_2,
  "4.3" => Version_4_3,
  "5.0" => Version_5_0,
  "5.1" => Version_5_1,
  "5.2" => Version_5_2,
  "6.0" => Version_6_0,
  "6.1" => Version_6_1,
}

Finally, create a new file called version_6_1.rb in the directory /opt/vagrant/embedded/gems/2.2.6/gems/vagrant-2.2.6/plugins/providers/virtualbox/driver. (On Windows, create this file in the folder C:\HashiCorp\Vagrant\embedded\gems\2.2.6\gems\vagrant-2.2.6\plugins\providers\virtualbox\driver.) In this new file, paste the content from here.

With these 3 changes, Vagrant 2.2.6 will work with VirtualBox 6.1.0. I hope this helps!