diff --git a/app/controllers/application.rb b/app/controllers/application.rb
--- a/app/controllers/application.rb
+++ b/app/controllers/application.rb
@@ -12,13 +12,13 @@
       return false
     end
 
-    user = User.find(session[:user_id])
     # check if run in single user mode
-    if (defined?(SINGLE_USER_MODE) and 
-        (SINGLE_USER_MODE) and
-        user.login != 'root')
-      redirect_to :controller => 'main', :action => 'login'
-      return false
+    if defined?(SINGLE_USER_MODE) and (SINGLE_USER_MODE)
+      user = User.find(session[:user_id])
+      if user==nil or user.login != 'root'
+        redirect_to :controller => 'main', :action => 'login'
+        return false
+      end
     end
 
     return true