I found the main problem, I had edited the wrong boost/config/user.hpp file. When I set BOOST_FILESYSTEM_DYN_LINK in the correct user.hpp file I get this error.

c:\Boost\include\boost-1_31\boost\config\auto_link.hpp(269): fatal error C1189: #error : "Mixing a dll boost library with a static runtime is a really bad idea..."

#if (defined(_DLL) || defined(_RTLDLL)) && defined(BOOST_DYN_LINK) # define BOOST_LIB_PREFIX #elif defined(BOOST_DYN_LINK) # error "Mixing a dll boost library with a static runtime is a really bad idea..." #else # define BOOST_LIB_PREFIX "lib" #endif

So wher am I supposed to set the _DLL symbol or do I need to disable auto_link. If so how?

The message tells you what you've done wrong: you can not use a dll that passes C++ objects between itself and your application unless you are also using a dll runtime library. If you do manage to do this your code will very likely crash and burn at runtime (due to recourses being allocated and freed by differing C++ runtimes). If you switch your code generation options (in the VC++ IDE) to use a dll runtime then the error message will go away. John.