This is with Windows 10, Vagrant 1.9.4 and VirtualBox 5.1.20.
This was working a week ago, so I'm not sure what happened. Since then, my workstation was updated with fixes and I updated from Vagrant 1.9.3 to 1.9.4.
==> balancer: Importing base box 'sles12sp1'...
==> balancer: Matching MAC address for NAT networking...
==> balancer: Setting the name of the VM: wasrepo
==> balancer: Clearing any previously set network interfaces...
==> balancer: Preparing network interfaces based on configuration...
balancer: Adapter 1: nat
balancer: Adapter 2: hostonly
==> balancer: Forwarding ports...
balancer: 22 (guest) => 2222 (host) (adapter 1)
balancer: 80 (guest) => 8080 (host) (adapter 1)
==> balancer: Running 'pre-boot' VM customizations...
==> balancer: Booting VM...
==> balancer: Waiting for machine to boot. This may take a few minutes...
balancer: SSH address:
127.0.0.1:2222 balancer: SSH username: vagrant
balancer: SSH auth method: private key
==> balancer: Running cleanup tasks for 'hosts' provisioner...
==> balancer: Forcing shutdown of VM...
==> balancer: Destroying VM and associated drives...
C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh/transport/server_version.rb:54:in `readpartial': An established connection was aborted by the software in your host machine. (Errno::ECONNABORTED)
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh/transport/server_version.rb:54:in `block (2 levels) in negotiate!'
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh/transport/server_version.rb:52:in `loop'
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh/transport/server_version.rb:52:in `block in negotiate!'
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh/transport/server_version.rb:50:in `loop'
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh/transport/server_version.rb:50:in `negotiate!'
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh/transport/server_version.rb:32:in `initialize'
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh/transport/session.rb:84:in `new'
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh/transport/session.rb:84:in `initialize'
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh.rb:233:in `new'
from C:/HashiCorp/Vagrant/embedded/gems/gems/net-ssh-4.1.0/lib/net/ssh.rb:233:in `start'
from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.9.4/plugins/communicators/ssh/communicator.rb:397:in `block (2 levels) in connect'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:88:in `block in timeout'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:32:in `block in catch'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:32:in `catch'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:32:in `catch'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:103:in `timeout'
from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.9.4/plugins/communicators/ssh/communicator.rb:371:in `block in connect'
from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.9.4/lib/vagrant/util/retryable.rb:17:in `retryable'
from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.9.4/plugins/communicators/ssh/communicator.rb:370:in `connect'
from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.9.4/plugins/communicators/ssh/communicator.rb:68:in `block in wait_for_ready'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:88:in `block in timeout'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:32:in `block in catch'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:32:in `catch'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:32:in `catch'
from C:/HashiCorp/Vagrant/embedded/lib/ruby/2.2.0/timeout.rb:103:in `timeout'
from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.9.4/plugins/communicators/ssh/communicator.rb:46:in `wait_for_ready'
from C:/HashiCorp/Vagrant/embedded/gems/gems/vagrant-1.9.4/lib/vagrant/action/builtin/wait_for_communicator.rb:16:in `block in call'