fnfErr -43 File or directory not found; incomplete pathname.
/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -background
path doest exist.
you can also use system command:
system("/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -background");
using NSTask:
NSTask *task;
task = [[NSTask alloc] init];
[task setLaunchPath: @"/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine"];
NSArray *arguments;
arguments = [NSArray arrayWithObject:@"-background"];
[task setArguments: arguments];
[task launch];