Try this:
Bitmap bitmap = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
success = false;
error="";
folder = folder.TrimEnd('\\');
try{
	Graphics graphics = Graphics.FromImage(bitmap as Image);
	graphics.CopyFromScreen(0, 0, 0, 0, bitmap.Size);
	if (bitmap != null)
	{
		bitmap.Save(@folder+"\\+fileName+"".png"");
		success = true;
	}
 }
catch(Exception e)
 {
 	error = e.ToString();
	success = false;
 }