I found why such a error occurs. According to your call "boost::regex_match(value, mr, ee)", the type of the first parameter is wstring (not const wchar_t*), and of the second is match_results<const wchar_t*>. So, the compiler selected the following overload from six. bool regex_match ( const std::basic_string<...>&, match_results < std::basic_string::const_iterator >&, const basic_regex<...>&, match_flag_type ) This overload requires a reference to match_results with std::basic_string::const_iterator template parameter. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This meens that the cast match_results < const wchar_t* >&, to match_results < std::basic_string::const_iterator >& was needed. Such a cast can be done successfully in VC6, but I think VC7.1's strict check did not allow it. Thanks. -*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*- TAKAHASHI Daisuke daisuke@ist.osaka-u.ac.jp -*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-