NullReferenceException when trying to set registry permissions with C# -

i'm trying set below permissions on registry key. nullreferenceexception error when tries. being novice makes tuff. throw in permissions (which have confused me) , i'm stumped. can tell me why i'm getting this? thanks.

using system; using microsoft.win32; using system.security.accesscontrol;  namespace consoleapplication7 {    class program    {        static void main(string[] args)        {            registrysecurity rs = new registrysecurity();            string user = "everyone";             registrykey rk = registry.localmachine.opensubkey(@"\software\wow6432node\123test", true);             rs.addaccessrule(new registryaccessrule(user,                registryrights.fullcontrol | registryrights.takeownership,                inheritanceflags.containerinherit,                propagationflags.none,                accesscontroltype.allow));             rk.setaccesscontrol(rs);        }    } } 

this line causing error

 registrykey rk = registry.localmachine.opensubkey(@"\software\wow6432node\123test", true); 

place debugger here , see if has value or null. if null check path valid. if valid this

registrykey rk = registry.localmachine.opensubkey(@"\\software\\wow6432node\\123test", true);