layer in menu singleton not displaying - cocos2d-iphone

Question

I have made a singleton to handle menu changes (navigating through menu hierarchy) in my game. I don't know why the menu is not displaying. Please see my MenuManager classes singleton below.
MenuManager.h:
#interface MenuManager : NSObject
{
MenuLayerTypes currentMenuLayer;
CCLayer* runningLayer;
CCLayer* oldLayer;
}
+(MenuManager*)sharedMenuManager;
-(void)runMenuWithID:(MenuLayerTypes)menuLayerID;
#end
MenuManager.m:
#import "MenuManager.h"
#implementation MenuManager
static MenuManager* _sharedMenuManager = nil;
+(MenuManager*)sharedMenuManager
{
#synchronized([MenuManager class])
{
if (!_sharedMenuManager)
[[self alloc] init];
return _sharedMenuManager;
}
return nil;
}
+(id)alloc
{
#synchronized ([MenuManager class])
{
NSAssert(_sharedMenuManager == nil,
#"Attempted to allocated a second instance of the Menu Manager singleton");
_sharedMenuManager = [super alloc];
return _sharedMenuManager;
}
return nil;
}
-(id)init
{
self = [super init];
if (self != nil)
{
Layer = kMainMenuLayer; // default menu type
}
return self;
}
-(void)runMenuWithID:(MenuLayerTypes)menuLayerID {
//MenuLayerTypes oldMenuLayer = currentMenuLayer;
currentMenuLayer = menuLayerID;
oldLayer.tag = 321;
switch (menuLayerID)
{
case kMainMenuLayer:
CCLOG(#"main menu layer");
runningLayer = [MainMenuLayer node];
oldLayer = runningLayer;
break;
case kSettingsLayer:
runningLayer = [SettingsLayer node];
oldLayer = runningLayer;
break;
case kAckLayer:
runningLayer = [AckLayer node];
oldLayer = runningLayer;
break;
default:
CCLOG(#"Unknown ID");
return;
break;
}
MainMenuScene* mainMenuScene = (MainMenuScene *)[[CCDirector sharedDirector] runningScene];
// checks to see if a menu layer is already displayed before replacing it
if (![mainMenuScene getChildByTag:321]) {
[mainMenuScene addChild:runningLayer];
}
else {
[mainMenuScene removeChildByTag:321];
[mainMenuScene addChild:runningLayer];
}
}
#end
Also in the init of the MainMenuScene:
[[MenuManager sharedMenuManager] runMenuWithID:kMainMenuLayer];
How can I solve this display issue?