Question

RegistryKey rkStartUp = Registry.CurrentUser;
RegistryKey StartupPath;
StartupPath =rkStartUp.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Run", true);
if (StartupPath.GetValue("MyApplication") == null)
{
    StartupPath.SetValue("MyApplication", Application.ExecutablePath, RegistryValueKind.ExpandString);
}
else
{
    StartupPath.DeleteValue("MyApplication", true);
}

Answer 1

First of all, be aware that registry keys are different for 32-bit and 64-bit systems. Also, in case your application is not running with admin rights, it is probably not permitted to write registry keys.