ASP.NET application error: "Unrecognized attribute 'targetFramework'"

You may experience the following error when you attempt to open your web application:
Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: Unrecognized attribute 'targetFramework'. Note that attribute names are case-sensitive.
The error indicates that your account is configured to use an older version of the ASP.Net framework.

To resolve the problem simply click the ASP.NET Version icon in the "Site Tools" section of Control Panel to switch to the correct framework. See this Knowledge Base article for more information.