Yes that is the site that is not working "I normally use the nightly build site" but am trying out the "more stable" alpha 1 build site, and it is bugged. Something on that dependency list is trying to connect to "
No repository found at http://download.jboss.org/jbosstools/updates/JBossTools-4.0.0.Alpha1b.core/."
which is causing the issue. Did that update site work for you??