ENOENT error using nodejs on heroku

I'm getting an ENOENT error on my heroku app, preventing it from starting up:

Error: ENOENT, open '/app/log/production.log'

This file / dir (app/log) does exist however... So I'm not sure what's going on?

I ended up disabling 'quiet' mode to stop writing logs to disk:

app.disable('quiet');

This seems to of resolved it