The boost.system documentation mentions a value_type typedef in boost::system::error_code several times in: http://www.boost.org/doc/libs/1_35_0/libs/system/doc/reference.html#Class-er... In ther header file there is no such typedef, just an int is used. I've filed a ticket here: http://svn.boost.org/trac/boost/ticket/2125 -- Arvid Norberg