I am configuring my web service with Web.config using windows
authentication.  I want to limit the web service permissions by using the
allow / deny roles authorization.  I have added the following in my
web.config:

  <authentication mode="Windows" />
   <authorization>
     <allow roles="Administrators"/>   <!-- I am assuming this can be
specified as a windows user group -->
     <deny users="*" />
  </authorization

When my application tries to make a call to the web service, I get a 401
error.  I have set the credentials on the request to use DefaultCredentials,
which I am assuming uses the logged on credentials.  The logon that I am
calling from is an Administrator calling the web service locally.  Why am I
getting a 401 error?  Is there something more that I need to do to allow my
logon to be able to call the local web service?