I am setting up confluence and I've found that I needed to use a very permissive java policy file.

Here are the contents:

> cat /etc/tomcat4/policy.d/06confluence.policy
grant codeBase "file:${catalina.home}/webapps/confluence/-" {
permission java.security.AllPermission;
};
// Yackkk!!!!!
grant {
permission java.lang.RuntimePermission "accessDeclaredMembers";
permission java.lang.reflect.ReflectPermission "suppressAccessChecks";
permission java.lang.RuntimePermission "defineCGLIBClassInJavaPackage";
};
>

This is apparently due to Hibernate.

Other found similar issues:
See <A HREF="http://www.javablogs.com/ViewEntry.jspa?id=85562">rant on hibernate</A>
and <A HREF="http://www.mail-archive.com/hibernate-devel@lists.sourceforge.net/msg02295.html">Hibernate security policy issues</A>