Thanks for the wiki link. :) You say that "The class loader isolation for each app ensures that user code can use JBC 2.x while the app server still uses 1.4.x for its own clustering." Recommend that you spell out how that class loader isolation was achieved -- that's the key piece of info readers need to understand. I'm guessing you did it just by putting JBC 2.x and all its dependencies in WEB-INF/lib and counting on the fact that a webapp uses a child-first classloader. Re: PojoCache vs core cache, when I look at the stack trace on http://www.jboss.com/index.html?module=bb&op=viewtopic&t=128465 I see it's failing in constructing a CacheImpl. That doesn't seem like something that would only fail in the PojoCache case. I suspect Pete hasn't done whatever you did to get the needed class loader isolation. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4131091#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...