The nightly JBoss tools site at http://download.jboss.org/jbosstools/builds/nightly/trunk/ has a latestBuild.html file that links to a nonexistant build:
http://download.jboss.org/jbosstools/builds/nightly/trunk/2010-09-29_22-55-10-H40/
This means that installing or updating from that site will fail.