diff --git a/.gitignore b/.gitignore
index 4349d8b..bdc750e 100755
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,4 @@
 *~
 .*.sw*
 old
-data/config.php
+data/
diff --git a/TODO b/TODO
index 9381b1d..dd16761 100755
--- a/TODO
+++ b/TODO
@@ -3,7 +3,6 @@
 * htmlspecialchars => on users objects
 * handle negative amounts
 * Refactor load method to avoir load_* methods !
-* Empêcher deux fois le même login
 
 install.php :
 =============
diff --git a/inc/Ban.inc.php b/inc/Ban.inc.php
index fb3337d..e9dcd4b 100644
--- a/inc/Ban.inc.php
+++ b/inc/Ban.inc.php
@@ -1,15 +1,15 @@
 <?php
     define('DATA_DIR', 'data'); // Data subdirectory
-    define('IPBANS_FILENAME', DATADIR.'/ipbans.php'); // File storage for failures and bans.
+    define('IPBANS_FILENAME', DATA_DIR.'/ipbans.php'); // File storage for failures and bans.
     define('BAN_AFTER', 5); // Ban IP after this many failures.
     define('BAN_DURATION', 1800); // Ban duration for IP address after login failures (in seconds) (1800 sec. = 30 minutes)
-    if (!is_dir(DATADIR)) { mkdir(DATADIR,0705); chmod(DATADIR,0705); }
-    if (!is_file(DATADIR.'/.htaccess')) { file_put_contents(DATADIR.'/.htaccess',"Allow from none\nDeny from all\n"); } // Protect data files.
+    if (!is_dir(DATA_DIR)) { mkdir(DATA_DIR,0705); chmod(DATA_DIR,0705); }
+    if (!is_file(DATA_DIR.'/.htaccess')) { file_put_contents(DATA_DIR.'/.htaccess',"Allow from none\nDeny from all\n"); } // Protect data files.
 
     function logm($message)
     {
         $t = strval(date('Y/m/d_H:i:s')).' - '.$_SERVER["REMOTE_ADDR"].' - '.strval($message)."\n";
-        file_put_contents(DATADIR.'/log.txt',$t,FILE_APPEND);
+        file_put_contents(DATA_DIR.'/log.txt',$t,FILE_APPEND);
     }
 
 
@@ -63,7 +63,7 @@
     }
 
     // Returns user IP
-    function user_IPs()
+    function user_ip()
     {
         $ip = $_SERVER["REMOTE_ADDR"];
         // Then we use more HTTP headers to prevent session hijacking from users behind the same proxy.
diff --git a/inc/User.class.php b/inc/User.class.php
index 6b551c5..1c633e0 100644
--- a/inc/User.class.php
+++ b/inc/User.class.php
@@ -120,4 +120,13 @@ class User extends Storage {
             return false;
         }
     }
+
+    public function isUnique() {
+        if(count($this->load_users(array('login'=>$this->login))) == 0) {
+            return true;
+        }
+        else {
+            return false;
+        }
+    }
 }
diff --git a/index.php b/index.php
index 28530fc..7104aab 100644
--- a/index.php
+++ b/index.php
@@ -6,7 +6,7 @@
     require_once('inc/Invoices.class.php');
     require_once('inc/rain.tpl.class.php');
     require_once('inc/functions.php');
-    require_once('inc/Banc.inc.php');
+    require_once('inc/Ban.inc.php');
     require_once('inc/CSRF.inc.php');
     raintpl::$tpl_dir = 'tpl/';
     raintpl::$cache_dir = 'tmp/';
@@ -150,10 +150,15 @@
                         $user->setPassword($user->encrypt($_POST['password']));
                     }
                     $user->setAdmin($_POST['admin']);
-                    $user->save();
 
-                    header('location: index.php?do=edit_users');
-                    exit();
+                    if($user->isUnique()) {
+                        $user->save();
+                        header('location: index.php?do=edit_users');
+                        exit();
+                    }
+                    else {
+                        $tpl->assign('error', 'A user with the same login exists. Choose a different login.');
+                    }
                 }
             }
  
diff --git a/tpl/edit_users.html b/tpl/edit_users.html
index 728823f..5ba3f47 100644
--- a/tpl/edit_users.html
+++ b/tpl/edit_users.html
@@ -29,6 +29,7 @@
 </table>
 {elseif condition="$view == 'edit_user'"}
 <h2>Edit a user</h2>
+{if condition="$error"}<p class="error">{$error}</p>{/if}
 <form method="post" action="index.php?do=add_user" id="edit_user_form">
     <p>
         <label for="login" class="label-block">Login : </label><input type="text" name="login" id="login" {if condition="$login_post != ''"} value="{$login_post}" {else} {$user_id != -1 ? 'value="'.$user_data->getLogin().'"' : ''} {/if}/>
diff --git a/tpl/settings.html b/tpl/settings.html
index 8f19e8d..cfbd41f 100644
--- a/tpl/settings.html
+++ b/tpl/settings.html
@@ -2,6 +2,7 @@
 
 {if condition="!$show_settings"}
 <h2>Edit homepage notice</h2>
+{if condition="$error"}<p class="error">{$error}</p>{/if}
 <form method="post" id="notice_form" action="index.php?do=edit_notice">
     <p>
         <label for="textarea_notice">Homepage notice :</label><br/>
@@ -15,8 +16,8 @@
 </form>
 
 {else}
-
 <h2>Change settings of your Bouffe@Ulm installation</h2>
+{if condition="$error"}<p class="error">{$error}</p>{/if}
 <form method="post" action="index.php?do=settings" id="settings_form">
     <fieldset>
         <legend>Database</legend>