Error in validation of managed_file field with Form API
There's a bug in the way system_settings_form() handles managed_file types. It's to do with the upload/remove buttons and parent elements (if you read the whole issue you hould get a good take on what's going on).

I don't know if it's the same error as I was having, but adding code like the following to the top of the form's submit handler fixed it for me:

foreach($form_state['buttons'] as $delta =&gt; &amp;$button) {
  if (preg_match('/module_top_content_equipe_image_(upload|remove)_button/i', $button['#name'])) {
      $button['#parents'] = array();
    }
  }


Not ideal by any means, but it does work.

On another note, the #process property attached to the managed_file item is unnecessary. That code should be run in the form's submit handler, and since your submit handler is named in the right convention it will be run when the form is submitted, which is when you need it to.

Try removing the #process line altogether and see what happens.