when you look at the java docs for the ldap callback, you'll notice that some of the parameters are mandatory. In fact both ldap.user.ctx and ldap.role.ctx are mandatory. So you need to specify what is the context in ldap that callback should search in for users and groups/roles. Once you specify that it should be able to access and fetch data correctly. You could simplify tests of the correct ldap settings by creating similar tests that jbpm has.
HTH