Hi there, I'm not actually sure this is a boost problem but I'll give it a try and ask for your opinion. Boost version is 1.36 I have a daemon here realising a web interface using pion and asio. Pion is also using asio. On Linux everything runs fine and I have my web interface, but using the same code on windows / vs 2005 I get the weirdest errors such as " Unhandled exception at 0x1004e55d in myapp.exe: 0xC0000005: Access violation reading location 0xcdcdcdd1." The debugger tells me this happens in function_template.hpp: #if !BOOST_WORKAROUND(BOOST_MSVC, < 1300) template<typename R BOOST_FUNCTION_COMMA BOOST_FUNCTION_TEMPLATE_PARMS> typename BOOST_FUNCTION_FUNCTION< R BOOST_FUNCTION_COMMA BOOST_FUNCTION_TEMPLATE_ARGS>::result_type BOOST_FUNCTION_FUNCTION<R BOOST_FUNCTION_COMMA BOOST_FUNCTION_TEMPLATE_ARGS> ::operator()(BOOST_FUNCTION_PARMS) const { if (this->empty()) boost::throw_exception(bad_function_call()); return static_cast<vtable_type*>(vtable)->invoker (this->functor BOOST_FUNCTION_COMMA BOOST_FUNCTION_ARGS); } #endif It says the static_cast rises the exception (?!) Damn MS. Anyway, I debugged into it and the last thing the debugger stepped into was in asio: size_t run(boost::system::error_code& ec) { if (::InterlockedExchangeAdd(&outstanding_work_, 0) == 0) { ec = boost::system::error_code(); return 0; } call_stack<win_iocp_io_service>::context ctx(this); size_t n = 0; while (do_one(true, ec)) if (n != (std::numeric_limits<size_t>::max)()) ++n; return n; } I don't know which line though. Can anyone help shed some light on this? Thanks and greetings... Stephan