Hi *! We switched the alignment of boost (1.34.0 + VC 7.1) libs to 4 byte, since our project has a restriction of 4byte struct member alignment and we receive a linker error that program_options can no link to a boost::program_options::arg string global. error LNK2001: unresolved external symbol "class std::basic_string const boost::program_options::arg" (?arg@program_options@boost@@3V?$basic_string@DU?$char_traits@D@std@ @V?$allocator@D@2@@std@@B) Making the dumpbin /exports from the boost_program_options....lib I clearly find this symbol as exported one, with the exactly searched signature. Using the default struct member alignment I can link to the program_options lib whithout any problems. Any ideas or suggestions are really welcome! With Kind Regards, Ovanes