I had the same problem. uninstalled the plugin, then deleted the S3 references in the .htaccess file from the uploads folder, and still had nothing working. I tried deactivating each plugin and reactivating it, still nothing. I even tried to reactivate the theme I use on top of the current activation, and nada. So now I am removing all files and starting over (i backed everything up first).
Anyone have any ideas why this happened or what I could have done differently?