Hello, I try to build the Boost 1.51 on the latest Cygwin version: I'm using this commands: export BZIP2_BINARY=bz2 export ZLIB_BINARY=z export ZLIB_INCLUDE=/cygdrive/c/Users/Administrator/Documents/zlib/1.2.7/include export ZLIB_LIBPATH=/cygdrive/c/Users/Administrator/Documents/zlib/1.2.7/lib export BZIP2_INCLUDE=/cygdrive/c/Users/Administrator/Documents/bzip2/1.0.6/include export BZIP2_LIBPATH=/cygdrive/c/Users/Administrator/Documents/bzip2/1.0.6/lib cd library/boost_1_51_0 ./bootstrap.sh ./b2 --with-exception --with-filesystem --with-math --with-random --with-regex --with-date_time --with-thread --with-system --with-program_options --with-serialization --with-iostreams --layout=system link=shared runtime-link=shared threading=multi variant=release install --prefix=../boost/1.51.0 ./boost/filesystem/path_traits.hpp: At global scope: ./boost/filesystem/path_traits.hpp:224: error: `std::wstring' has not been declared ./boost/filesystem/path_traits.hpp:228: error: ISO C++ forbids declaration of `to' with no type In file included from ./boost/filesystem/operations.hpp:25, from libs\filesystem\src\unique_path.cpp:20: ./boost/filesystem/path.hpp:378: error: ISO C++ forbids declaration of `wstring' with no type ./boost/filesystem/path.hpp:378: error: invalid use of `::' ./boost/filesystem/path.hpp:378: error: expected `;' before '&' token ./boost/filesystem/path.hpp:379: error: expected `;' before "const" ./boost/filesystem/path.hpp:379: error: ISO C++ forbids declaration of `wstring' with no type ./boost/filesystem/path.hpp:379: error: invalid use of `::' ./boost/filesystem/path.hpp:379: error: expected `;' before '&' token ./boost/filesystem/path.hpp:400: error: expected `;' before "template" ./boost/filesystem/path.hpp:409: error: ISO C++ forbids declaration of `wstring' with no type ./boost/filesystem/path.hpp:409: error: invalid use of `::' ./boost/filesystem/path.hpp:409: error: expected `;' before "generic_wstring" ... The Boost filesystem is not build on the command the full build process is stop with the error Is this an error on my installation and how can I solve the problem? Thanks a lot Phil