diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -47,12 +47,17 @@
 
     # check if run in single user mode
     if GraderConfiguration[SINGLE_USER_MODE_CONF_KEY]
-      user = User.find(session[:user_id])
+      user = User.find_by_id(session[:user_id])
       if user==nil or (not user.admin?)
         flash[:notice] = 'You cannot log in at this time'
         redirect_to :controller => 'main', :action => 'login'
         return false
       end
+      unless user.enabled?
+        flash[:notice] = 'Your account is disabled'
+        redirect_to :controller => 'main', :action => 'login'
+        return false
+      end
       return true
     end