Stuck on using uinavigationcontroller

Question

I am creating a navigation project on IPhone SDK. In briefly, my project can do a log in action. After I click a log-in button to log in. It crashes.... I Found that it failed in

DisclaimerController *disclaimerController = [[DisclaimerController alloc] initWithNibName:@"DisclaimerPage" bundle:nil];

UIViewController *targetViewController = disclaimerController; [[self navigationController] pushViewController:targetViewController animated:YES]; [targetViewController release];

after that I change it to

DisclaimerController *disclaimerController = [[DisclaimerController alloc] init];

no crash anymore.

but no contents show in the page??

Please help me..

Thanks for all kind people.