IdentityPermissions

When using the identity permissions for declarative code access
security I find that there are two overloaded methods for the
constructor described in the msdn library, these methods are for
permission states and for strings.

public UrlIdentityPermission(PermissionState state);

public UrlIdentityPermission(string site);

When I attempt to code the permission (eg, UrlIdentityPermission) it
requires a SecurityAction and says that the string constructor does
not exist.

Does anyone know why this is or how to specify a site address in the
urlIdentityPermission?

Thankyou,

Kerry