Hello, I am compiling a program which uses the program_options library, and I am getting an unresolved symbol (boost::program_options::arg class std::basic_string ). This is using the vc-7_1 toolset (boost 1.33.1, bjam --v2). I don't have such problem on Linux g++ 3.4.4 I see it in the value_semantic.cpp. If I play with setting I can get it to compile, but it sends a warning 'inconsistent linkage', and later crashes on dbgheap.hpp I have compiled program_options with --v2 -stoolset=vc-7_1 -slink=shared -sthreading=multi -svariant=debug, and the same with my program. I've also added -sruntime-link=dynamic, same problem. Are there other options that need to be set before compiling program_options? Where is arg going to be defined if its external? I know it's something I'm doing wrong, can someone please help. Thanks Matthieu