Erro...não sei o que é...

Ai pessoal sou iniciante aqui...gostaria que exclarecece minha duvida....não sei pq na minha aplicaçãooo esta dando esse erro aquiServer Error in '/' Application.--------------------------------------------------------------------------------Configuration Error Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately. Parser Error Message: It is an error to use a section registered as allowDefinition='MachineToApplication' beyond application level. This error can be caused by a virtual directory not being configured as an application in IIS.Source Error: Line 49: ASP.NET to identify an incoming user. Line 50: -->Line 51: <authentication mode='Windows'/>Line 52: <!--Line 53: The <customErrors> section enables configuration Source File: C:\SERVER VIRTUAL\website1\web.config Line: 51 --------------------------------------------------------------------------------Version Information: Microsoft .NET Framework Version:2.0.50727.42; ASP.NET Version:2.0.50727.210