iPhone和模拟器上存在EXC_BAD_ACCESS问题

- (void)locationManager:(CLLocationManager *)manager 
didUpdateToLocation:(CLLocation *)newLocation 
       fromLocation:(CLLocation *)oldLocation
{
    NSLog(@\"At new location: %@\",newLocation);

    MKCoordinateRegion region = 
            MKCoordinateRegionMakeWithDistance([newLocation coordinate], 750, 750);

    [mapView setRegion:region animated:YES];
    [location stopUpdatingLocation];

    CLLocationCoordinate2D coord = [newLocation coordinate];
    NSURL *url = [urlCache getReccomendationForUID:@\"12345\" atLat:coord.latitude 
                                         atLon:coord.longitude forCategories:nil];


    // Create the request.
    NSURLRequest *request = [NSURLRequest requestWithURL:url
                                         cachePolicy:NSURLRequestUseProtocolCachePolicy
                                     timeoutInterval:60.0];


// create the connection with the request
// and start loading the data
    connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:YES];
    if (connection) {
        // Create the NSMutableData to hold the received data.
        // xmlData is an instance variable declared elsewhere.
        xmlData = [[NSMutableData alloc]init];
    } else {
        NSLog(@\"Could not create connection\");
    }
}

-(NSURL *)getReccomendationForUID:(NSString *)u atLat:(double)lat atLon:(double)lon forCategories:(NSArray *)cat
{
    if(remote) {
        NSMutableString *categories = [[NSMutableString alloc]init];
        for(NSString *s in cat) {
            [categories appendString:@\"&cat=\"];
            [categories appendString:s];
        }
        NSString *s = [NSString stringWithFormat:@\"%@/recommendation?uid=%@&psw=null&lat=%f&lon=%f?%@\",
                   apiRoot,u,lat,lon,categories];
        [categories release];
        return [NSURL URLWithString:s];
    } else {
        return [[NSBundle mainBundle] URLForResource:@\"XMLTest\" withExtension:@\"xml\"];;
    }
}