我把_UNICODE 红用于C运行期头文件，为什么会有link错误？

windonws2000; VC6下
为了使CString支持unicode,我在
project->setting->c/c++->preprocessor definition 中将_MBCS替换为_UNICODE
编译后发生link error:msvcrtd.lib(crtexew.obj) : error LNK2001: unresolved external symbol _WinMain@16
Debug/test4.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.who know the reason? thanks much.