Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 23297)
+++ wp-includes/user.php	(working copy)
@@ -91,8 +91,8 @@
 
 	if ( is_multisite() ) {
 		// Is user marked as spam?
-		if ( 1 == $user->spam)
-			return new WP_Error('invalid_username', __('<strong>ERROR</strong>: Your account has been marked as a spammer.'));
+		if ( 1 == $user->spam )
+			return new WP_Error('spammer_account', __('<strong>ERROR</strong>: Your account has been marked as a spammer.'));
 
 		// Is a user's blog marked as spam?
 		if ( !is_super_admin( $user->ID ) && isset($user->primary_blog) ) {