Website hosted in Plesk on Windows fails to load: Service Temporarily Unavailable

Symptoms

• The website returns an error such as the following when accessed via a browser:
   

  CONFIG_TEXT: Service Temporarily Unavailable
  The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

• The website in Plesk is not with a Suspended status.

• The site under the IIS pool for the domain does not return any errors on restart
• The domain is configured correctly to resolve to the IP address of the server

Cause

An invalid or corrupted web.config file within the main directory of the website prevents its IIS application pool for this domain from running as expected, due to which it crashes repeatedly.

Resolution

1. Log into Plesk
2. Rename the web.config file under website's main directory to web.config.backup via the Plesk File Manager
3. Start Command Prompt as an Administrator

4. Run the following command in order to force the recreation of a default web.config file:

   C:\> plesk repair web example.com -y

5. The error on the website will change, but it will likely still fail to load, because your script likely requires a specific configuration to exist within its web.config file
6. Analyze the web.config file, compare it to the web.config.backup file from earlier and make sure to add only the necessary content from the web.config.backup back to the web.config file and save the changes.
7. Restart the application pool for the website in IIS
8. Confirm that the website is now loading as expected