I've seen info in various email-threads regarding thread safety when using xml archives. We had come across some assert conditions in multithreaded code, only to trace down that (BOOST_SPIRIT_THREADSAFE) was not defined during boost compilation. to fix, I modified the Jamfile.v2 for serialization: lib boost_serialization : $(SOURCES).cpp /boost/thread//boost_thread # needed to add this as a dep b/c we need to link threads when we define BOOST_SPIRIT_THREADSAFE : <define>BOOST_SPIRIT_THREADSAFE # needed to add this as a define <toolset>msvc:<cxxflags>/Gy <link>shared:<define>BOOST_SERIALIZATION_DYN_LINK=1 <conditional>@include-spirit ; I've also added BOOST_SPIRIT_THREADSAFE as a <define> in our code as well. I hope this helps others... Cheers, Tim