I would recommend tracing with the debugger trough serialization of optional<string> in portable binary archive to see how it's different from serialization in binary or text archive.
I've performed a bit more analysis and it looks like serialization of optional<> with any non-trivial types is broken in 1.64. The serialization/optional.hpp load function: template<class Archive, class T> void load( Archive & ar, boost::optional< T > & t, const unsigned int /*version*/ )[...] In 1.63, constructed space for the type with: detail::stack_construct<Archive, T> aux(ar, item_version); ar >> boost::serialization::make_nvp("value", aux.reference()); t.reset(aux.reference()); which ensures the constructor is called. However, for 1.64 this changed to: detail::stack_allocate<T> tp; // <<<<<<<<<<<<<< ar >> boost::serialization::make_nvp("value", tp.reference()); t.reset(boost::move(tp.reference())); ar.reset_object_address( t.get_ptr(), & tp.reference() ); Unfortunately, this only allocates (zero'd) space for the object, and some objects (in this case, std::string in g++ 4.6) are not valid as such. I see that in 1.65 this changed again, to the simpler: if(! t.is_initialized()) t = T(); ar >> boost::serialization::make_nvp("value", *t); It seems I was just unlucky to choose 1.64. I've moved to 1.66 and it's all working. -- Sent from: http://boost.2283326.n4.nabble.com/Boost-Users-f2553780.html