[AndyD]

Попробуй так

            void LoadKeyboardLayout()
            {
                dll dll = new dll("user32");
                dllFunction dllFunction = new dllFunction(dll, "LoadKeyboardLayoutA");
                #define.KLF_ACTIVATE(1)
                ;
                dllFunction.arg(ExtTypes::String, ExtTypes::DWord);
                dllFunction.returns(ExtTypes::DWord);
                dllFunction.call("00000419", #KLF_ACTIVATE);
            }

PS А в твоем коде надо заменить Word'ы на DWord'ы