problems with uinavigationcontroller

[maxmxmaxmx]

i have a problem with the navigationcontroller. i like to push and pop between 2 viewcontrollers. it starts with the first, pushes to the second, pops back an the next push is not working. so pushing from the 1. to the 2. again

- (void)pushFirstToSecond{
	[self.navController popViewControllerAnimated:NO];
	[self.navController pushViewController:[[AppViewController alloc] autorelease] animated:NO];
}
- (void)pushBackFromSecondToFirst{
        //setting up a new instance of the first view
	MainView *contentV = [[MainView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]];
	[contentV setImage:[UIImage imageNamed:@"background.png"]];
	[contentV loadVariables];
	MainViewController *mainControll = [[MainViewController alloc] init];
	[mainControll setView:contentV];
	[contentV setUserInteractionEnabled:YES];
	UIViewController *controll= mainControll;
	UIViewController *viewC = [self.navController topViewController];
	[self.navController popViewControllerAnimated:NO];
	[self.navController pushViewController:controll animated:NO];
        //dont know if i need to release the view of viewC
	//[viewC releaseView];
	[viewC release];
}

somehow its not working and it seems to be that the second viewcontroller is not released at the time i push it again
because if i dont stop the sounds of it i still hear it operate
i think it pushes back automatically because it still says pushBackFromSecondToFirst if its on the top of the stack.
but if i try to release the view its throwing exeptions.

could some one please help me out
thank you!