self.tableView reloadData breaks it

[hazelnut]

i hope somebody can help me. i want to fetch a json file and update a tableview with the data. that's my .h

PHP Code:

@interface FirstViewController : UITableViewController {
    UITableView *tableView;    
    NSDictionary *listData;    
    NSMutableData *responseData;
}
@property (nonatomic, retain) NSDictionary *listData;
@property (nonatomic, retain) NSMutableData *responseData;
@property (nonatomic, retain) IBOutlet UITableView *tableView; 


and my .m

PHP Code:

@synthesize listData;
@synthesize responseData;
@synthesize tableView;

- (void)viewDidLoad 
{
    self.listData = nil;

    // load external data    
    responseData = [[NSMutableData data] retain];
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://JSON_URL"]];
    [[NSURLConnection alloc] initWithRequest:request delegate:self];
    
    [super viewDidLoad];
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    [responseData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    [responseData appendData:data];
}
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"Connection failed: %@", [error description]);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    [connection release];
    
    NSError *error = nil;
    NSDictionary *dictionary = [[CJSONDeserializer deserializer] deserializeAsDictionary:responseData error:&error];
    
    self.listData = dictionary;
    
    [self.tableView reloadData]; // <--------- breaks it, but why??
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return 1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [self.listData count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    
    static NSString *CellIdentifier = @"CustomCell";
    CustomCell *cell = (CustomCell *) [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        
        NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:@"CustomCell" owner:self options:nil];
        
        for (id currentObject in topLevelObjects){
            if ([currentObject isKindOfClass:[UITableViewCell class]]){
                cell =  (CustomCell *) currentObject;
                break;
            }
        }
    }
    
    return cell;
}
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}
- (void)dealloc {
    [responseData release];
    [listData release];
    [super dealloc];
} 


after fetching the json data (connectionDidFinishLoading) the [self.tableView reloadData] breaks the app. but why? i've read in so many posts that that is the way the reload a tableview (?)

thanks for any help