Updating in case anyone finds this helpful. The simple solution is that j2ee.jar was missing from the classpath.
I just migrated from
Java 1.4 to Java 1.5 and from Tomcat 4 to Tomcat 5 and Sun does not have a
j2ee distribution for 1.5 yet (at least not that i could find).
so whereas the j2ee.jar was in my Sun/AppServer/lib path before when starting tomcat4, it was not part of the java lib when starting tomcat 5 because java 1.5 lib did not come with j2ee.jar
JR