When setting new coordinates for MKPointAnnotation the pin disappears

Question

When I try to move my MKPointAnnoatation like this:

[UIView animateWithDuration:0.5 animations:^{
            [user setCoordinate:coordinate];

The pin disappears on the map :( Is there a different solution to move a MKPointAnnotion?

EDIT MORE CODE:

CLLocationCoordinate2D *plotLocation = malloc(sizeof(CLLocationCoordinate2D) *
                                              _trak.trakTagRelationship.count);

    int i=0;
    for (TrakTag* tag in _trak.trakTagRelationship)
    {

        CLLocationCoordinate2D coordinate = CLLocationCoordinate2DMake(tag.trakTagX.doubleValue,
                                                                           tag.trakTagY.doubleValue);
        plotLocation[i] = coordinate;


        i++;
    }

    TrakTag* dummy = [[_trak.trakTagRelationship allObjects]lastObject];
    CLLocationCoordinate2D coordinate = CLLocationCoordinate2DMake(dummy.trakTagX.doubleValue,
                                        dummy.trakTagY.doubleValue);

    if (user != NULL)
    {
        [UIView animateWithDuration:0.5 animations:^{
            [user setCoordinate:coordinate];

            NSLog(@"Annotaions:%@",user);

        }];
    }
    else
    {
        user = [[MKPointAnnotation alloc]init];
        [user setCoordinate:coordinate];
        [mapView addAnnotation:user];
    }


    line = [MKPolyline polylineWithCoordinates:plotLocation count:_trak.trakTagRelationship.count];
    [mapView addOverlay:line];