PLEASE PLEASE HELP - Castor porblem

[Gandu]

I am a newbie to the Castor library. As per the instructions at the
exolab site,
I have added the paths of the relevant jar files to the CLASSPATH.
However,
whenever I type in:
D:\Castor\org\exolab\castor\builder>java
org.exolab.castor.builder.SourceGenerator -i
D:\\Castor\org\exolab\castor\dsml\schema\dsml.xsd

I get the error message:

Exception in thread "main" java.lang.NoClassDefFoundError:
org/apache/xml/serialize/XMLSerializer
at org.exolab.castor.builder.BuilderConfiguration.load(BuilderConfiguration.java:440)
at org.exolab.castor.builder.BuilderConfiguration.getDefault(BuilderConfiguration.java:247)
at org.exolab.castor.builder.BuilderConfiguration.<init>(BuilderConfiguration.java:233)
at org.exolab.castor.builder.SourceGenerator.<init>(SourceGenerator.java:272)
at org.exolab.castor.builder.SourceGenerator.<init>(SourceGenerator.java:261)
at org.exolab.castor.builder.SourceGenerator.<init>(SourceGenerator.java:252)
at org.exolab.castor.builder.SourceGenerator.main(SourceGenerator.java:708)
Could someone please help me?