Exception in org.jboss.tools.jst.web.kb.internal.KbProject@162d74e

#1 import project https://svn.jboss.org/repos/jbosstools/trunk/documentation/whatsnew into workspace
#2 call clean and build
an exception will occurs(Failed to process class path in kb builder for project org.jboss.tools.jst.web.kb.internal.KbProject@162d74e, An exception stack trace is not available.)