I have some schema files I generate Java classes from using Castor. A snippet from my maven.xml looks like: <attainGoal name="castor:prepare-filesystem"/> <castor:generate schema="${maven.src.dir}/xsd/adapter.script.xsd" package="com.piplusplus.messaging.configuration"/> When I use JDK 1.3.1 it generates the source correctly. When using any of the newer Java versions I instead get the following obscure error: java.lang.NoClassDefFoundError: sun/reflect/ConstructorAccessorImpl I tried adding the "-X" and "-verbose:class" options to track the problem further and also tried debugging against with the Castor source in my path. I think I began to make some progress, but subsequently gave up. From memory it was having problems unmarshalling the "simple types" (or similar) properties file. After much lost time I found that the problem was avoided by causing the invokation of the source generator to be done in a forked process. This can be achieved by pretending to have a Castor properties file by adding the line "maven.castor.properties.dir=." to the "project.properties" file, which is the workaround I'm currently using. I've also added a patch to always fork, rather than only when a Castor properties file is available. If "someone" could take a look at what I've done and commit if appropriate I'd be appreciative. If not, then at least if I save someone's time I'd be happy too. I like Maven, but it can be difficult to debug certain problems that occur.