diff -Naur WebCalendar-1.2.3.orig/includes/menu/index.php WebCalendar-1.2.3.new/includes/menu/index.php
--- WebCalendar-1.2.3.orig/includes/menu/index.php	2011-04-19 13:08:51.178088428 +0200
+++ WebCalendar-1.2.3.new/includes/menu/index.php	2011-04-19 13:18:19.466766130 +0200
@@ -70,7 +70,7 @@
     $year_url .= '?user=' . $user;
 
     if ( ! empty ( $new_entry_url ) )
-      $new_entry_url .= '&user=' . $user;
+      $new_entry_url .= (strpos($new_entry_url, '?') !== FALSE? '&': '?') . 'user=' . $user;
 
     if ( ! empty ( $new_task_url ) )
       $new_task_url .= '&user=' . $user;