Configuring latest Pluto 2.0 for Tomcat 6.x

Any advice?  I have an installation of Pluto 2.0 + Tomcat 6.0.16 from
back in the spring that works fine.  Now I am trying to install the
latest Pluto 2.0 into either a new Tomcat 6.0.16 or Tomcat 6.0.18.  All
seems to install okay (based on the information from the Pluto
website).  However Pluto doesn't start -- becaused it throws a
noClassDefFound exception for the class:
org.apache.pluto.driver.PortalStartupListener.  Checking the various
config files makes it look like things are set up right.  And of course
this class exists in the pluto-portal-driver-2.0.0-SNAPSHOT.jar that is
found in the web-inf/lib dir of the pluto (installed) webapp.  Has
anyone seen this/or have ideas on what I can check/try?
     -Mike-