Hi, I've got the linker error LNK2005 (http://msdn.microsoft.com/en-us/library/72zdcz6f(VS.80).aspx) using MSVC80 (Studio 2005): libboost_program_options-vc80-mt-1_35.lib(value_semantic.obj) : error LNK2005: "public: __thiscall boost::program_options::invalid_option_value::invalid_option_value(class std::basic_string const &)" (??0invalid_option_value@program_options@boost@@QAE@ABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(value_semantic.obj) : error LNK2005: "public: virtual char const * __thiscall boost::program_options::validation_error::what(void)const " (?what@validation_error@program_options@boost@@UBEPBDXZ) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(value_semantic.obj) : error LNK2005: "void __cdecl boost::program_options::validate(class boost::any &,class std::vector,class std::allocator > > const &,class std::basic_string *,int)" (?validate@program_options@boost@@YAXAAVany@2@ABV?$vector@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@PAV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@5@H@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(value_semantic.obj) : error LNK2005: "private: virtual void __thiscall boost::program_options::value_semantic_codecvt_helper<char>::parse(class boost::any &,class std::vector,class std::allocator > > const &,bool)const " (?parse@?$value_semantic_codecvt_helper@D@program_options@boost@@EBEXAAVany@3@ABV?$vector@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@_N@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(options_description.obj) : error LNK2005: "public: class boost::program_options::options_description_easy_init __thiscall boost::program_options::options_description::add_options(void)" (?add_options@options_description@program_options@boost@@QAE?AVoptions_description_easy_init@23@XZ) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(options_description.obj) : error LNK2005: "class std::basic_ostream & __cdecl boost::program_options::operator<<(class std::basic_ostream &,class boost::program_options::options_description const &)" (??6program_options@boost@@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV23@ABVoptions_description@01@@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(options_description.obj) : error LNK2005: "public: __thiscall boost::program_options::options_description::options_description(unsigned int)" (??0options_description@program_options@boost@@QAE@I@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(options_description.obj) : error LNK2005: "public: __thiscall boost::program_options::options_description::options_description(class std::basic_string const &,unsigned int)" (??0options_description@program_options@boost@@QAE@ABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@I@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(options_description.obj) : error LNK2005: "public: class boost::program_options::options_description_easy_init & __thiscall boost::program_options::options_description_easy_init::operator()(char const *,char const *)" (??Roptions_description_easy_init@program_options@boost@@QAEAAV012@PBD0@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(options_description.obj) : error LNK2005: "public: class boost::program_options::options_description_easy_init & __thiscall boost::program_options::options_description_easy_init::operator()(char const *,class boost::program_options::value_semantic const *,char const *)" (??Roptions_description_easy_init@program_options@boost@@QAEAAV012@PBDPBVvalue_semantic@12@0@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(options_description.obj) : error LNK2005: "public: class boost::program_options::options_description & __thiscall boost::program_options::options_description::add(class boost::program_options::options_description const &)" (?add@options_description@program_options@boost@@QAEAAV123@ABV123@@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. libboost_program_options-vc80-mt-1_35.lib(convert.obj) : error LNK2005: "class std::basic_string __cdecl boost::program_options::to_internal(class std::basic_string const &)" (?to_internal@program_options@boost@@YA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@ABV34@@Z) ist bereits in boost_program_options-vc80-mt-1_35.lib(boost_program_options-vc80-mt-1_35.dll) definiert. using the linker options: /O2 /Ob2 /I "C:\Cpp\boost_1_35_0" /I ... /D "WIN32" /D "_WINDOWS" /D "NDEBUG" /D "BOOST_ENABLE_ASSERT_HANDLER=1" /D "QT_DLL" /D "QT_GUI_LIB" /D "QT_CORE_LIB" /D "QT_NO_DEBUG" /D "CMAKE_INTDIR=\"Release\"" /D "_MBCS" /FD /EHsc /MD /Fo"eda.dir\Release\\" /Fd"D:/work/build/Release/eda.pdb" /W3 /nologo /c /TP /errorReport:prompt Any ideas what happened here? Thanks, Olaf