I just deleted one of my cached boxes to test a change and now I can't bring it back up:
$ vagrant up 0s
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Box 'mandrel-api' could not be found. Attempting to find and install...
default: Box Provider: virtualbox
default: Box Version: >= 0
==> default: Box file was not detected as metadata. Adding it directly...
==> default: Adding box 'mandrel-api' (v0) for provider: virtualbox
/opt/vagrant/embedded/lib/ruby/2.2.0/fileutils.rb:1444:in `rmdir': Directory not empty @ dir_s_rmdir - /Users/robwilkerson/.vagrant.d/tmp/vagrant-box-add-temp-20160522-1576-e94ngb (Errno::ENOTEMPTY)
I've reinstalled Vagrant (1.8.1), deleted my project's .vagrant/ directory and even deleted my ~/.vagrant.d directory. Totally desperate right now if anyone can help.