This error reads:
The web server is not configured correctly. See help for common configuration errors. Running the web page outside of the debugger may provide further information.
Possible causes of this error include:
Trying to debug a .NET web application that was copied to a different machine, manually renamed, or moved.
Not having enough IIS connections. (See "Limiting Connections" in the IIS Operations Guide.)
If you are trying to debug an ASP.NET project
Check to see that the DEBUG verb is associated with .aspx. See How to: Associate DEBUG Verb with Extension for more information.
Check to see that the Web site has been configured as an Application in IIS.
From the Start menu, choose Programs, then Administrative Tools, and click Internet Information Services.
In the Internet Information Services dialog box, click the tree control for your machine, open the Web Sites folder, and find your web site.
Right-click Web Site and choose Properties.
In the Web Site Properties window, select the Directory tab.
Under Application Settings, look for the Remove or Create button.
If the button says Remove, your website is already configured as an application.
If the button says Create, click the button to configure your website as an application.
Click OK.
If you are trying to debug an ATL Web application
Reference