Colum Lynch: the U.N. Bars Taiwanese Official From Briefing claiming it's because of the organization's "one-China" policy. But

the press club has hosted briefings by the Chinese spiritual group Falun Gong, Irish Republican Army members, Chechen rebels and other individuals and organizations whose appearances offended member states. Annan's action today raised concern that other governments would be emboldened to prevent their critics from addressing reporters at U.N. headquarters...

...China's efforts to bar Hsia from addressing reporters have drawn greater attention to Taiwan's cause.

Another reason to ridicule the UN.