This issue occurs due to the pipeline mode in your application pool settings that your website is set to.
In this method, two procedures can be applied;
- Change the Application Pool mode the one that has classic pipeline enabled. This adds the following line of codes;
<validation validateIntegratedModeConfiguration="false" />
- Your web.config will be needed to alter to support the integrated pipelines. This is as simple as removing the parts of your web.config.
The use of the first approach is bad practice. So, it is suggested to use the second approach.
The best solution is to change your application to support the integrated pipelines. There is a number of changes between the IIS6 and IIS7.x that will raise an error message.
If you are unable to do that then you have to change the App pool which may be more difficult to do and totally depends upon the availability of your web server.
- Go to the webserver.
- Open the IIS manager.
- Navigate to your site.
- Click on the Advanced Settings on the right Action pane.
- Under Application Pool, change it to the app pool that has classic enabled.
If you can access the server after these changes, then do this through the hosted server and contact them for help.