问NSTimer内存错误

EN

@property (nonatomic, retain) NSTimer* refreshTimer;

- (id) init
{
    self = [super init];
    if (self != nil) 
    {
        self.refreshTimer = [NSTimer timerWithTimeInterval:600 target:self selector:@selector(timerRefreshGPS:) userInfo:nil repeats:YES];
        [[NSRunLoop currentRunLoop] addTimer:refreshTimer forMode:NSDefaultRunLoopMode];
    }
    return self;
}

-(void) updateUserGPSLocation:(CLLocation*)newLocation
{
    [refreshTimer invalidate];
    [refreshTimer release];
    self.refreshTimer = nil; 

    self.refreshTimer = [NSTimer timerWithTimeInterval:600 target:self selector:@selector(timerRefreshGPS:) userInfo:nil repeats:YES];
    [[NSRunLoop currentRunLoop] addTimer:refreshTimer forMode:NSDefaultRunLoopMode];
}

- (void)dealloc 
{
    [refreshTimer invalidate];
    [refreshTimer release];
    self.refreshTimer = nil; 
    [super dealloc];
}