I fixed the problem. For debug: my project setting as: C/C++ > Code Generation > Runtime LIbrary as "Multi-threaded DLL (/MD)" But in my release setting: C/C++ > Code Generation > Runtime LIbrary as "Multi-threaded (/MT)" When I changed it to "Multi-threaded DLL (/MD)", then it works! As indicated in the boost/boost/config/user.hpp, which needs _DLL flag. Thanks, Maggie ---------- Forwarded message ---------- From: maggie.nguyen@gmail.com <maggie.nguyen@gmail.com> Date: Sep 29, 2006 9:45 AM Subject: boost regex library problem with release build To: Hi, I use Visual Studios 2005. In my project file, I include the library in linker: "Additional Library Directories: ..\..\boost\lib" I have these libs in the boost\lib directory: libboost_date_time-vc80-mt-1_33_1.lib libboost_date_time-vc80-mt-gd-1_33_1.lib libboost_regex-vc80-mt-1_33_1.lib libboost_regex-vc80-mt-gd-1_33_1.lib libboost_thread-vc80-mt-1_33_1.lib libboost_thread-vc80-mt-gd-1_33_1.lib When I build my project as a debug build. it compiles fine. However, if I change to release build, it gives me this error: Error 1 fatal error LNK1104: cannot open file 'libboost_regex-vc80-mt-s-1_33_1.lib' Please let me know what I need to do to have it point to "libboost_regex-vc80-mt-1_33_1.lib" instead of "libboost_regex-vc80-mt-s-1_33_1.lib". Thanks very much, Maggie