Brennan’s Blog

When you are doing web development with ASP.NET 2.0 you may use the website configuration tool inside Visual Studio. You access it on the file menu at Website - ASP.NET Configuration. When you do so you can configure multiple options which are then stored in your web.config. Unfortunately doing so will break support for Intellisense. What it does is place an xmlns attribute into the configuration element to point to the schema. If you leave it in place you will lose Intellisense support. It can safely removed to restore Intellisense.

For more detail, read Scott Guthrie's post on the topic.