Index: branches/Ver2.4/xpressme_integration_kit/include/oninstall.php
===================================================================
--- branches/Ver2.4/xpressme_integration_kit/include/oninstall.php	(revision 793)
+++ branches/Ver2.4/xpressme_integration_kit/include/oninstall.php	(revision 794)
@@ -161,4 +161,6 @@
 	$pass_md5 = is_object($GLOBALS["xoopsUser"])?$GLOBALS["xoopsUser"]->getVar("pass"):'';
 	
+	add_filter('sanitize_user', "sanitize_user_multibyte" ,10,3);
+	
 	if (!function_exists('username_exists')){
 		require_once($mydirpath . '/wp-includes/registration-functions.php');
@@ -296,3 +298,16 @@
 }
 endif;
+if( ! function_exists( 'sanitize_user_multibyte' ) ) :
+function sanitize_user_multibyte($username, $raw_username, $strict){
+	if ($username == "" && $strict){
+		if ($raw_username == ""){
+			return $username;
+		} else{
+			return sanitize_user($raw_username, false);
+		}
+	} else {
+		return $username;
+	}
+}
+endif;
 ?>
Index: branches/Ver2.4/xpressme_integration_kit/wp-content/plugins/xpressme/xpressme.php
===================================================================
--- branches/Ver2.4/xpressme_integration_kit/wp-content/plugins/xpressme/xpressme.php	(revision 793)
+++ branches/Ver2.4/xpressme_integration_kit/wp-content/plugins/xpressme/xpressme.php	(revision 794)
@@ -82,4 +82,20 @@
  	}
 }
+
+// enable multibyte username
+if( ! function_exists( 'sanitize_user_multibyte' ) ){
+	function sanitize_user_multibyte($username, $raw_username, $strict){
+		if ($username == "" && $strict){
+			if ($raw_username == ""){
+				return $username;
+			} else{
+				return sanitize_user($raw_username, false);
+			}
+		} else {
+			return $username;
+		}
+	}
+}
+add_filter('sanitize_user', "sanitize_user_multibyte" ,10,3);
 
 add_action('admin_menu', 'my_plugin_menu');