Hi Andreas, First off you need to open the offending class (org.hibernate.hql.ast.tree.FromClause) and then locate addDuplicateAlias method, and then just put the fromElementByClassAlias.put( alias, element ); call into an if statement like so: | void addDuplicateAlias(String alias, FromElement element) { | if(alias != null) { | fromElementByClassAlias.put( alias, element ); | } | } | This solution has not been verified by the hibernate people, but if you look in the method above addDuplicateAlias(registerFromElement) they always perform the hashmap.put() calls in an if statement checking that the "key" (classAlias) is not null. This got rid of my problem, hopefully it should do the same for you. After you have modified the source, rebuild with ant, i would use the target "jar" or "dist" Let me know how you get on with it. Cheers, Andy View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4000511#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...