Partial fix when a portal have a lot of users, we need something prettier but xajax works see #4127 An error occurred

main/admin/add_users_to_session.php

@@ -45,7 +45,8 @@ $tbl_class_user						= Database::get_main_table(TABLE_MAIN_CLASS_USER);
 // setting the name of the tool
 $tool_name = get_lang('SubscribeUsersToSession');
 
-$add_type = 'multiple';
+$add_type = 'unique';
+
 if(isset($_REQUEST['add_type']) && $_REQUEST['add_type']!=''){
 	$add_type = Security::remove_XSS($_REQUEST['add_type']);
 }
@@ -291,6 +292,7 @@ if ($ajax_search) {
 				}
 			}
 		}
+        
 		if ($use_extra_fields) {
 			$final_result = array();
 			if (count($extra_field_result)>1) {
@@ -353,7 +355,7 @@ if ($ajax_search) {
 
 		$result   = Database::query($sql);
 		$Users    = Database::store_result($result);
-		//var_dump($_REQUEST['id_session']);
+
 		foreach ($Users as $user) {
 			if($user['id_session'] != $id_session)
 				$nosessionUsersList[$user['user_id']] = $user ;