Elastic Beanstalk Invalid Parameter Value

I was getting a fairly ambiguous error from my app.config elastic beanstalk configuration file.

app.config

option_settings:
   - namespace: aws:elasticbeanstalk:application:environment
     option_name: NODE_ENV
     value: production
   - namespace: aws:elasticbeanstalk:container:nodejs:staticfiles
     option_name: /public
     value: /public
   - namespace: aws:elasticbeanstalk:container:nodejs
     option_name: NodeVersion
     value: 0.10.26
packages: 
  yum:
    GraphicsMagick: []
files:
    "/etc/nginx/conf.d/proxy.conf" :
        mode: "000755"
        owner: root
        group: root
        content: |
           client_max_body_size 10M;

command line

> eb create --cfg med-env-sc
...
Printing Status:
INFO: createEnvironment is starting.
INFO: Using elasticbeanstalk-us-east-1-466215906046 as Amazon S3 storage bucket for environment data.
ERROR: InvalidParameterValue: Parameter values must be a string or a list of strings
ERROR: Failed to launch environment.
ERROR: Failed to launch environment.