Index: src/wp-admin/includes/misc.php
===================================================================
--- src/wp-admin/includes/misc.php	(revision 25799)
+++ src/wp-admin/includes/misc.php	(working copy)
@@ -296,8 +296,8 @@
  */
 function show_message($message) {
 	if ( is_wp_error($message) ){
-		if ( $message->get_error_data() && is_string( $message->get_error_data() ) )
-			$message = $message->get_error_message() . ': ' . $message->get_error_data();
+		if ( $message->get_error_data() )
+			$message = $message->get_error_message() . ': ' . implode( ", ", (array) $message->get_error_data() );
 		else
 			$message = $message->get_error_message();
 	}