I'm trying to get our system working with xalan-J 2.6.0 (we used an older version yet) but I get this:

java.lang.NoSuchMethodError
at org.apache.xml.dtm.ref.dom2dtm.DOM2DTM.addNode(DOM2DTM.java:259)

The most likely reason is that there are multiple jars with
conflicting Xalan versions are in the classpath.

I'm working with Tomcat-3.3.

This can easily happen in web applications, because the servlet
container adds several non-obvious directories to the search path
for jars. You'll have to search these directories and remove any
unwanted jar. The exact details depend on your environment. Note
that this is already off-topic for this list, you may get more help
on the appropriate Tomcat lists.