Configuration Error - Unrecognized attribute 'xmlns' web.config - ASP.net 2.0

When you try running a ASP.net 2.0 web application, you may receive a web.config error as "Unrecognized attribute 'xmlns'"

Line 1: <?xml version="1.0"?>
Line 2:
Line 3: <configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">
Line 4:

Reason
Your system/server must be running more than one version of .net framework

Resolution
1. Choose Start -> Control Panel -> Administrative Tools -> Internet Information Services
2. Expand the nodes until you can see your virtual directory
3. Right-click on the virtual directory and click Properties
4. Select the ASP.NET tab
5. Under the ASP.NET version, choose 2.0.50215.0
6. Click OK.