TypeError: Bad argument

When I do "markdown-pdf -o test.pdf test.md", I get this.

TypeError: Bad argument
at TypeError (native)
at ChildProcess.spawn (internal/child_process.js:289:26)
at exports.spawn (child_process.js:380:9)
at Object.exports.execFile (child_process.js:143:15)
at WriteStream. (C:\Program Files\nodejs\node_modules\markdown-pdf\index.js:117:22)
at emitNone (events.js:91:20)
at WriteStream.emit (events.js:185:7)
at finishMaybe (_stream_writable.js:515:14)
at endWritable (_stream_writable.js:525:3)
at WriteStream.Writable.end (_stream_writable.js:490:5)

Granted, I used npmbox to build an offline installer for this. But if I'm missing something, I'd really like to know what. Don't deal with node.js and npm stuff everyday. Any clues would be helpful.