I have tried to upgrade from 7.0 to 7.1 but it failed. After upgrading, my login form is not displayed. When I opened the website after copying all files from the upgrade package to the server, the upgrade wizard was not started but the default page was displayed directly. Prior to upgrading I was using the Darkknight skin for the site. I was not able to stop the application using the app_offline.htam method prior to copying the files to the server. How can I solve the problem?