iPhone PopToRootViewController and immediately push a new view controller

Try

UINavigationController * navigationController = self.navigationController;
[navigationController popToRootViewControllerAnimated:NO];
LoginViewController *loginViewController = [[[LoginViewController alloc] initWithNibName:@"TableView" bundle:nil] autorelease];
[navigationController pushViewController:loginViewController animated:YES];

I think your bit of code comes from a view controller which is in the navigation stack, so the popToRootViewControllerAnimated: message set the navigationController property to nil, thus the pushViewController:animated: message is sent to nil.