Thanx for your reply.
I've managed to get it correctly by coding like this:
ManagementScope sc = (ManagementScope)scope.Clone();
sc.Path.NamespacePath = "root\\default"; //StdRegProv is in there
ManagementPath path = new ManagementPath(string.Format(@"\\{0}\root\Default:StdRegProv", sc.Path.Server));
regClass = new ManagementClass(sc, path, null);
Scope is initialized earlier like this
ConnectionOptions c = new ConnectionOptions();
c.Username = "User";
c.Password = "Password";
c.Authentication = AuthenticationLevel.Default;
string path = @"\\Myserver\root\cimv2";
scope = new ManagementScope(path, c);
scope.Connect();
//path is init to ...cimv2 b/c I use it for other objects too