Lost Intelllisense in web.config in Visual Studio

If you lost your intellisense in Visual Studio in the web.config file, it is probably because your configuration element, right at the top of the web.config file, has a xmlns attribute, like this:

To restore the Intellisense just delete the namespace declaration so that the configuration element has no attributes, like so:

That namespace declaration can be added by the Web Configuration tool, for example, or any other tool, or developer that might have meddled with the xml on the file.