XercesParser: class is not found

[Symeon Jacobson <q9...@mail.connect.usq.edu.au>]

I am running apache-1.3.9-4, ApacheJServ 1.1 and Cocoon 1.7.2.  I get the
following error from any request for an xml document:

java.lang.RuntimeException: Error creating = org.apache.cocoon.parser.XercesParser: class is not found
at java.lang.Throwable.(Throwable.java:40)
at java.lang.Exception.(Exception.java:21)
at java.lang.RuntimeException.(RuntimeException.java:21)
at org.apache.cocoon.framework.Manager.create(Manager.java:106)
at org.apache.cocoon.Engine.(Engine.java:129)
at org.apache.cocoon.Engine.getInstance(Engine.java:196)
at org.apache.cocoon.Cocoon.init(Cocoon.java:119)
at org.apache.jserv.JServServletManager.load_init(JServServletManager.java:569)
at org.apache.jserv.JServServletManager.loadServlet(JServServletManager.java:488)
at org.apache.jserv.JServConnection.processRequest(JServConnection.java:266)
at org.apache.jserv.JServConnection.run(JServConnection.java:188)
at java.lang.Thread.run(Thread.java:241)

The logs show org.apache.cocoon.Cocoon as having started, and XercesParser
is in the same .jar file as Cocoon so it shouldnt be a classpath issue.  How
can this happen, and more importantly how can I fix it?
Thx.