Undefined Index when adding a new field to any Content Type or Taxonomy
Sounds like an issue with your current Drupal version


  A patch to fix this has been committed to 7.x and will be available in
  7.15. In the meantime, visiting the image field settings form and clicking Save will resolve the issue


More info: http://drupal.org/node/1558548
Patch here: http://drupal.org/files/drupal-1558548-3.patch