--- wp-includes/user.php.ori	2011-11-11 11:43:03.538728700 +0100
+++ wp-includes/user.php	2011-12-05 07:14:57.806032700 +0100
@@ -93,7 +93,7 @@
 	if ( is_multisite() ) {
 		// Is user marked as spam?
 		if ( 1 == $userdata->spam)
-			return new WP_Error('invalid_username', __('<strong>ERROR</strong>: Your account has been marked as a spammer.'));
+			return new WP_Error('spammer_username', __('<strong>ERROR</strong>: Your account has been marked as a spammer.'));
 
 		// Is a user's blog marked as spam?
 		if ( !is_super_admin( $userdata->ID ) && isset($userdata->primary_blog) ) {