Help on Preprocessing views field

Hi, I am preprocessing my view field (event calendar view), where I have the followings:

(1) view name= calendar,
(2) Current_display = block_2, and
(3) I have 'event_calendar_date' (event date) field that I would like to preprocess.

I have the following code:

function MyTheme_preprocess_views_view_fields(&$vars) {
	$view = $vars['view'];
	
	if($view->name=='calendar' && $view->current_display=='block_2') {
		foreach ($vars['fields'] as $id=>$field) {
			if($id == 'event_calendar_date'') {
				$vars['fields'][$id]->content = 'some text ';
			}
		}
	}
}

Have I missed something here? It is not working.

Thanks,
Maadis.