There is an error in boost/asio/error.hpp in HEAD - definition of boost::asio::detail::error_base<T>::misc_ecat is unavailable on Windows build. The solution is to move #endif from line 103 to line 98. The following patch works for me: Index: error.hpp =================================================================== RCS file: /cvsroot/boost/boost/boost/asio/error.hpp,v retrieving revision 1.11 diff -u -r1.11 error.hpp --- error.hpp 9 Jan 2007 13:54:51 -0000 1.11 +++ error.hpp 13 Jan 2007 04:18:33 -0000 @@ -95,12 +95,12 @@ static std::string addrinfo_md(const boost::system::error_code& ec); static boost::system::wstring_t addrinfo_wmd( const boost::system::error_code& ec); +#endif // !defined(BOOST_WINDOWS) && !defined(__CYGWIN__) static boost::system::error_category misc_ecat; static int misc_ed(const boost::system::error_code& ec); static std::string misc_md(const boost::system::error_code& ec); static boost::system::wstring_t misc_wmd(const boost::system::error_code& ec); -#endif // !defined(BOOST_WINDOWS) && !defined(__CYGWIN__) static boost::system::error_category ssl_ecat; static int ssl_ed(const boost::system::error_code& ec); -- Pavel