Starnet blocking is what United Airlines does to minimize/eliminate awards that Mileage Plus members can use; basically, United has decided that it doesn't want to allow many *A awards on partner carriers and thus has directed its IT department to make many/most *A awards invisible to the UA reservations agents. Makes one wonder why UA has any "partners" at all. Now that I write that, makes one wonder why UA is allowed in the *A at all. Anyway, also see
here.