How can I avoid EXC_BAD_ACCESS when checking if directories exist?

I'm building an app which caches images in the Documents directory of the app bundle. In order to make sure the directories exist, I want to check to see if they exist and, if they don't, create them at the point at which the application starts.

Currently, I'm doing this in didFinishLaunchingWithOptions: like so:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    NSArray *directoriesToCreate = [[NSArray alloc] initWithObjects:
                                    @"DirA/DirA1",
                                    @"DirA/DirA2",
                                    @"DirB/DirB2",
                                    @"DirB/DirB2",
                                    @"DirC",
                                    nil];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsPath = [paths objectAtIndex:0];

    for (NSString *directoryToCreate in directoriesToCreate) {

        NSString *directoryPath = [documentsPath stringByAppendingPathComponent:directoryToCreate];
        NSLog(directoryPath);
        if (![[NSFileManager defaultManager] fileExistsAtPath:directoryPath isDirectory:YES]) {

            NSError *directoryCreateError = nil;
            [[NSFileManager defaultManager] createDirectoryAtPath:directoryPath
                                      withIntermediateDirectories:YES
                                                       attributes:nil
                                                            error:&directoryCreateError];


        }

    }

    [window addSubview:navigationController.view];
    [window makeKeyAndVisible];

    return YES;

}

On the very first run of the application – when none of the directories exist – the application runs, the directories are created as expected and everything runs just fine.

When the application is terminated, and runs again, I get an EXC_BAD_ACCESS signal on the fileExistsAtPath: call on [NSFileManager defaultManager].

What I don't understand is why this runs just fine when the directories don't exist, but it falls over when they do exist.

Can anyone offer any assistance?