The configuration section 'security' cannot be read because it is missing a section declaration

I am trying to add to the web.config the following section:

<location path="Test.aspx">
<system.web>
 <security>
    <authentication>
      <anonymousAuthentication enabled="false" />
      <windowsAuthentication enabled="true" />
    </authentication>
  </security>
</system.web>
</location>

But I get error "The configuration section 'security' cannot be read because it is missing a section declaration"

What am I doing wrong?