>You must write WIN32API instead USER32 when you declare the Api.

There's no such requirement. You can either specify exact name of DLL that hosts API functions or WIN32API which will cause VFP to search in Kernel32.dll, Gdi32.dll, User32.dll, Mpr.dll, and Advapi32.dll. The first one is faster and only a choice if DLL isn't in the above list.