Symptoms
The example.com website fails to load with error 500.19:
CONFIG_TEXT: Configuration file is not well-formed XML
Cause
Website's %plesk_vhosts%example.comhttpdocsweb.config file is invalid
Resolution
Make sure that the web.config file is configured correctly. Online tools such as https://elmah.io/tools/configvalidator/ can help with the troubleshooting.