Error "MachineToApplication" when open solution with VS

Few years ago (2005), a colleague created a VS2005 project an "Web Application" and not a "Web site". Now I have to do some change

When I open the solution, I get this error :

It is an error to use a section registered as allowDefinition='MachineToAp开发者_如何学JAVAplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS.

I'd like use the Visual Studio web server. How can I solve this problem ?

Thanks,

Update 1 : (web.config localisation) http://i54.tinypic.com/2vtw7xk.png

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Confirm that your web.config file is in the root directory.