QCF Design Community

I loaded up the beta page for the first time in quite a while today, and the Unity auto-update page fails with Chrome, Firefox and IE on Windows Vista. Browsers and OS should be relatively up-to-date.
Unity Plugin version:2.5.1f5
Unity Engine version:3.3.0f4

That's quite strange... Have you tried updating the plugin directly from the Unity site?

http://unity3d.com/webplayer/