error en el debug

[fabi_hola_7]

hola a todos... me surgio un problema con mi aplicacion ojala ustedes sepan de que se trata este error que me muestra cuando abro la aplicacion "The web server reported the following error when attempting to create or open the web project located at the following URL: 'http//localhost/aplicacion', 'HTTP/1.1 500 Internal Server Error'". Hago click en aceptar y carga la aplicacion pero cuando quiero correr la aplicacion manda este otro error "Error while trying to run project: Unable to star debugging on the web server. Server side-error ocurred on sendind debug HTTP request. Make sure the server is operating correctly. Verify there are not syntax errors in web.config by doing a debug.start without Debugging. you may also want to refer to the ASP.NET and ATL server debugging topic in the online documentation."