This callback is weird... it is called in addition to the `done()` callback inside the GearJS task. It used to cause a `process.exit(1)` here through the `log.error` call. However it has some additional logging so I figured I may as well keep it to perform that logging and let the `done()` callback fail the queue (and eventually trickle back to the original call to `init()`/`add()`).