The Windows SDK comes with the full development system of CVI. And it gets installed under /bin/sdk. Assuming you have it installed, make sure you include the file before CVI's header file , in case you are using the latter. Do not include winuser.h by itself. There are several necessary macros that windows.h defines for you. Besides, windows.h includes winuser.h. Give it a try.
Regards,
Azucena Perez
National Instruments