I am calling a method that goes in a background thread:

[self performSelectorInBackground:@selector(loadViewControllerWithIndex:) withObject:[NSNumber numberWithInt:viewControllerIndex]];

then, I have this method implementation that gets called by the selector:

- (void) loadViewControllerWithIndex:(NSNumber *)indexNumberObj {
    NSAutoreleasePool *arPool = [[NSAutoreleasePool alloc] init];
    NSInteger vcIndex = [indexNumberObj intValue];

    Class c;
    UIViewController *controller = [viewControllers objectAtIndex:vcIndex];

    switch (vcIndex) {
    	case 0:
    		c = [MyFirstViewController class];
    		break;
    	case 1:
    		c = [MySecondViewController class];
    		break;
    	default:
    		NSLog(@"unknown index for loading view controller: %d", vcIndex); // error
    		break;
    }

    if ((NSNull *)controller == [NSNull null]) {
    	controller = [[c alloc] initWithNib];
    	[viewControllers replaceObjectAtIndex:vcIndex withObject:controller];
    	[controller release];
    }

    if (controller.view.superview == nil) {
    	UIView *placeholderView = [viewControllerPlaceholderViews objectAtIndex:vcIndex];
    	[placeholderView addSubview:controller.view];
    }

    [arPool release];
}

Althoug I do create an autorelease pool there for that thread, I always get this error:

2009-05-30 12:03:09.910 Demo[1827:3f03] *** _NSAutoreleaseNoPool(): Object 0x523e50 of class NSCFNumber autoreleased with no pool in place - just leaking
Stack: (0x95c83f0f 0x95b90442 0x28d3 0x2d42 0x95b96e0d 0x95b969b4 0x93a00155 0x93a00012)

If I take away the autorelease pool, I get a whole bunch of messages like these. I also tried to create an autorelease pool around the call of the performSelectorInBackground:, but that doesn't help.

I suspect the parameter, but I don't know why the compiler complains about an NSCFNumber. Am I missing something?

My Instance variables are all "nonatomic". Can that be a problem?

UPDATE: I may also suspect that some variable has been added to an autorelease pool of the main thread (maybe an ivar), and now it trys to release that one inside the wrong autorelease pool? If so, how could I fix that? (damn, this threading stuff is complex ;) )