Hi, I'm having some issues linking my code with the 64-bit version of boost 1.51 on windows with VC 10. I managed to write this small example that illustrates my problem. It is a project to create a DLL. I downloaded from boostpro.com. Here's the code: #include <boost/regex.hpp> #include <boost/filesystem.hpp> void useBoost() { } and the result. ------ Build started: Project: test-64, Configuration: Release x64 ------ UsesRegex.cpp UsesRegex.obj : error LNK2001: unresolved external symbol "class boost::system::error_category const & __cdecl boost::system::system_category(void)" (?system_category@system@boost@ @YAAEBVerror_category@12@XZ) UsesRegex.obj : error LNK2001: unresolved external symbol "class boost::system::error_category const & __cdecl boost::system::generic_category(void)" (?generic_category@system@boost@ @YAAEBVerror_category@12@XZ) C:\Users\aleblanc\projects\trunk\XDE\sandbox\alain\c-testing\test-64\x64\Release\test-64.dll : fatal error LNK1120: 2 unresolved externals ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== However, if I comment out the include for filesystem.hpp it compiles ok. I have included the path to the boost libraries in the 'Additional Library Directories' property for the linker. otherwise it complains about not finding the library for boost_regex. Compiling for 32 bit (with the path for the libraries to a 32-bit installation of boost) works fine. Any suggestion would be appreciated. Thanks, a