boost::thread error

Hi,
when i try to include <boost/thread.hpp> to my project i gets:

error LNK2019: unresolved external symbol "class boost::system::error_category const & __cdecl boost::system::system_category(void)" (?system_category@system@boost@@YAABVerror_category@12@XZ) referenced in function "public: __thiscall boost::thread_exception::thread_exception(int,char const *)" (??0thread_exception@boost@@QAE@HPBD@Z)

i work with other boost libs fine.

i have VS2010, win 7, 64 bit.