Hi, This is (yet another) question about the archive_exception::unregistered_class ("derived class not registered or exported"). I've tried to find as much information before posting here, but frankly I'm stumped at this point. I believe this SO topic (http://stackoverflow.com/questions/9189055/put-the-serialization-of-a-class-...) is pretty much the exact same problem I'm having if you want more code to look at. The problem is that the archive_exception::unregistered_class exception is thrown when attempting to serialize via a base class pointer that is instantiated as a derived type defined in a shared library (DLL). The declaration and definition for the serialization is split between a header/cpp respectively. Serializing in the same manner, but with the derived class defined in the same executable works correctly. To hopefully answer the easy questions right away: the header contains the BOOST_CLASS_EXPORT_KEY macro and the cpp contains the BOOST_CLASS_EXPORT_IMPLEMENT with the defined exported templated functions for the binary_iarchive and binary_oarchive, e.g.: header: BOOST_CLASS_EXPORT_KEY(derivedClass) cpp: BOOST_CLASS_EXPORT_IMPLEMENT(derivedClass) template LIB_LINKAGE void derivedClass::serialize(boost::archive::binary_iarchive & ar, const unsigned int version); template LIB_LINKAGE void derivedClass::serialize(boost::archive::binary_oarchive & ar, const unsigned int version); The derivedClass::serialize contains the serialization for the base class, e.g.: template <class Archive> void ModuleStarted::serialize(Archive & ar, unsigned int) { ar & boost::serialization::base_object<baseClass>(*this); } My problem only exists under msvc (have not tried other versions but using 9 with SP1), building under g++ 4.6.3 works correctly. I have tested with Boost 1.49.0 and 1.50.0. Some discussions mentioned placing the BOOST_CLASS_EXPORT_* macros after the export.hpp #include, and even having the export.hpp included after the archive headers, all of which don't appear to work. I have also created a standalone VS solution with the executable and dll projects from the Boost.Serialization test code (test_dll_export, with polymorphic_base and polymorphic_derived2) and the same problem still occurs. I have attached this file (unfortunately the include paths will need to be modified) - it's built against Boost 1.50.0. I've looked at the following discussions: http://www.boost.org/doc/libs/1_50_0/libs/serialization/doc/special.html#dll... (The manual, I've triple-checked this). http://lists.boost.org/boost-users/2011/01/65295.php (Robert modified a VS solution but the zip was never attached properly, so I cannot check this). Thanks, Mark