Cannot edit field collections: Attempt to update field Fieldname failed:

I confirm same bug (using field collection 7.x-1.x). I have no idea why and when it happen, but my field collection instances does not have indexes inside data column. That's why it throws error on field collection save.

I made a small workaround which will allow you to save your field collection. The only place I could add indexes was to field data was hook_field_update_forbid (from its name it does not seem that it serves for these needs, but another hook hook_field_read_field which is there too does not allow to change the data... strange behavior from drupal core... :( ).

Anyway, here's what I made:

/**
 * Implements hook_field_update_forbid().
 */
function hook_field_update_forbid(&$field, &$prior_field, &$has_data) {
  if($prior_field['module'] == 'field_collection') {
    if(empty($prior_field['indexes'])) {
      $prior_field['indexes'] = array(
        'revision_id' => array('revision_id')
      );
    }
  }
}

You will need this only once, to save your collection field. Then you won't need it anymore for this specific field collection.

This is just a workaround. Guys from Field Collection team need to find what's the problem if this strange behavior. Maybe it has something to do with the nested field collections? I do not have any idea and do not have time to test it. But the issue exists!!

Yes, I think this is a dupe of #2141781: Existing index issue with revision_id index