I'm currently using 1_33_1 I've been having some problems with serialization so I built a test module that serializes a set of class template instantiations in a way that vaguely matches my real application. The template instances are derived classes from a common pure virtual base class. I got it to work properly in the test app, but then noticed I hadn't done BOOST_IS_ABSTRACT or BOOST_CLASS_EXPORT for the template instantiations like I had in my real classes. When I add BOOST_IS_ABSTRACT for the derived template instantiations, it compiles, but then crashes in save_pointer because bpos_ptr is NULL. The initial failure is higher in the call stack at boost::archive::detail::save_pointer_type<>::invoke (oserializer.hpp), where it requests the bpos_ptr from register_type. I realize NOW that it's probably performing as expected (except there's no assert) since the derived class is NOT abstract. I had run into problems (much) earlier where it appeared that I needed the BOOST_IS_ABSTRACT on the derived classes and not the base class but that may have been a side effect of other things I was doing wrong. It had not appeared to be a problem using the superfluous BOOST_IS_ABSTRACT until recently (switch to 1_33_1?). I note that the boost cvs tip version (for 1_34) also does not have an assert there. I'm not sure if that would have helped me figure out what was wrong, but at least an assert would terminate things closer to the source of the problem... Anyway - perhaps this will help someone else who's running into the NULL bpos_ptr problem... Thanks for your great work and support on the forum here! Hugh Hoover Enumclaw Software.