invalid option --sourcemap="auto"

There is another question like this one, but it mentions Ruby.

I am using npm/grunt to compile sass and I get this invalid option error when running my watch task.

Here is the chunk of my Gruntfile:

sass: {
dist: {
  options: {
    style: 'expanded',
    sourcemap: 'auto',
    //compass: true - may revive this at some point
  },
  files: [{
    expand: true,
    cwd: './',
    src: ['*.scss'],
    dest: '../../',
    ext: '.css'
  }]
}
},

Sass version:

$ sass -v
Sass 3.2.9 (Media Mark)

This used to work when I had it running on a different server and after a fresh install last night, the error is suddenly there. I can comment out the line to get work done, but I'd like to know why it's failing. Thanks.

via JacobIRR