RuntimeError: midiOutOpen: Unspecified when selecting output on Windows

[mydoghasworms]

This happens on Windows (10, not sure if that makes a difference). Ruby version is ruby 1.9.3p448 (2013-06-27) [i386-mingw32].

irb(main):001:0> require 'unimidi'
=> true
irb(main):002:0>  @output = UniMIDI::Output.gets

Select a MIDI output...
0) Microsoft GS Wavetable Synth
> 0
RuntimeError: midiOutOpen: Unspecified
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/midi-winmm-0.1.10/lib/midi-winmm/map.rb:217:in `winmm_func'
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/midi-winmm-0.1.10/lib/midi-winmm/output.rb:18:in `enable'
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/unimidi-0.4.6/lib/unimidi/device.rb:121:in `open'
        from C:/Ruby193/lib/ruby/gems/1.9.1/gems/unimidi-0.4.6/lib/unimidi/device.rb:49:in `gets'
        from (irb):2
        from C:/Ruby193/bin/irb:12:in `<main>'