Proble on xdoclet and bundled ant.

When I use bundled ant to execute my xdoclet task, it always prompts me with error message: "taskdef A class needed by class xdoclet.modules.ejb.EjbDocletTask cannot be found: xjavadoc/ant/XJavadocTask", unless I add the xdoclet lib dir to the additional classpath tab. But if I use the external ant within IDEA, everything is ok. So anything I did wrongly? I realy want to setup everything ok in build.xml instead of add some classpath through IDEA UI.