Hi everybody:

when I make the web.config file to make the authentication and the 
autherization for my web site.

the code is as following:

<configuration>
    <appSettings/>
    <connectionStrings/>
    <system.web>
      <authentication mode="Forms">
        <forms  name="Default" loginUrl="~/Default.aspx" />
      </authentication>
    </system.web>
</configuration>

But when I dubbge my page I recive the following 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.

the red line is :

<authentication mode="Forms">