#include <boost/date_time/posix_time/posix_time.hpp> #include <boost/asio.hpp> produces the error message at compile time: 1>c:\boost_1_37_0\boost\asio\detail\socket_types.hpp(27) : fatal error C1189: #error : WinSock.h has already been included while #include <boost/asio.hpp> #include <boost/date_time/posix_time/posix_time.hpp> does not. Same problem occurs when including any of the headers in boost/thread/... Robert Ramey